sio nanoparticle to optimize the colloidal suspension
TRANSCRIPT
SiO2 Nanoparticle to Optimize the Colloidal Suspension Stability and Filter Cake Buildup in Water-Based
Mud
Johanna Vargas Clavijo
Universidad Nacional de Colombia
Facultad de Minas, Departamento de Procesos y Energía
Medellín, Colombia
2021
SiO2 Nanoparticle to Optimize the Colloidal Suspension Stability and Filter Cake Buildup in Water-Based
Mud
Johanna Vargas Clavijo
Tesis presentada(o) como requisito parcial para optar al título de:
Doctor en Ingeniería – Sistemas Energéticos
Director (a):
Ph.D., M.Sc., Ingeniero de Petróleos, Sergio Hernando Lopera Castro
Codirector (a):
Ph.D., M.Sc., Ingeniero Químico, Farid Bernardo Cortés Correa
Línea de Investigación:
Nanotecnología aplicada al mejoramiento de fluidos de perforación
Grupo de Investigación:
Grupo de Investigación en Yacimientos de Hidrocarburos
Grupo de Investigación en Fenómenos de Superficie “Michael Polanyi”
Universidad Nacional de Colombia
Facultad de Minas, Departamento de Procesos y Energía
Ciudad, Colombia
2021
A mis padres y hermanos por su apoyo
incondicional y permitirme ser como soy.
"Solo si nos detenemos a pensar en las
pequeñas cosas llegaremos a comprender las
grandes".
José Saramago
Declaración de obra original
Yo declaro lo siguiente:
He leído el Acuerdo 035 de 2003 del Consejo Académico de la Universidad Nacional.
«Reglamento sobre propiedad intelectual» y la Normatividad Nacional relacionada al
respeto de los derechos de autor. Esta disertación representa mi trabajo original, excepto
donde he reconocido las ideas, las palabras, o materiales de otros autores.
Cuando se han presentado ideas o palabras de otros autores en esta disertación, he
realizado su respectivo reconocimiento aplicando correctamente los esquemas de citas y
referencias bibliográficas en el estilo requerido.
He obtenido el permiso del autor o editor para incluir cualquier material con derechos de
autor (por ejemplo, tablas, figuras, instrumentos de encuesta o grandes porciones de
texto).
Por último, he sometido esta disertación a la herramienta de integridad académica, definida
por la universidad.
______________________________
Nombre: Johanna Vargas Clavijo
Acknowledgments
I would like to express my gratitude to my two academic advisors, Prof. Sergio H. Lopera
and Prof. Farid B. Cortés, for their guidance and support in these years. I am grateful to
have them in my Ph.D. career.
Special acknowledgments to the research group members in Hydrocarbon Reservoirs and
the Surface Phenomena “Michael Polanyi” research group for their support.
I also want to acknowledge Dr. Maen Hussein from the University of Calgary for sharing
their expertise and their valuable contributions.
Special acknowledge to COLCIENCIAS for the support provided in agreement 785 of 2018.
Also, Universidad Nacional de Colombia for logistical and financial support.
Thanks to those who accompanied me day and night and were a reason for overcoming
and perseverance, parents, siblings, grandpa, and Marcos. Thanks to my college friends
for sharing the research ideas and life with me. Thanks to Ecomares Club´s female
underwater rugby team and coaches for the loyalty and support.
Resumen y Abstract IX
Resumen
Nanopartículas de SiO2 para optimizar la estabilidad de la suspensión coloidal y la
formación del revoque en lodos base agua
La aglomeración y el proceso de filtración en suspensiones coloidales ocurre en muchos
fenómenos naturales y aplicaciones de ingeniería. El problema más común de la teoría
coloidal es la estabilización de una dispersión; reducción de la aglomeración mediante el
control de las fuerzas entre partículas. Si las partículas se aglomeran, los tamaños de
aglomerados aumentan, aumentando la velocidad de sedimentación (o deposición) de
forma aleatoria en la superficie. Los fluidos de perforación están compuestos por un fluido
base, agua y partículas sólidas suspendidas, carbonato de calcio - CaCO3. En la mayoría
de los casos, se utilizan polímeros para favorecer la dispersión del material sólido. Sin
embargo, factores como la contaminación del lodo, el tamaño, la concentración de sólidos,
los cambios de pH, etc., pueden alterar la carga superficial y afectar la estabilidad coloidal
y alterar las propiedades del fluido de perforación. Una alternativa a la mejora actual de
las propiedades de los fluidos de perforación es el uso de la nanotecnología. Sin embargo,
pocos estudios teóricos están disponibles en la literatura u omiten las interacciones entre
partículas para dichas suspensiones coloidales. De esta forma, la tesis se centra
principalmente en la estabilidad coloidal en el sistema polímero-CaCO3 y el
empaquetamiento sólido en el proceso de filtración en presencia de nanopartículas (NPs).
Las NP de sílice (SiO2) son un material común y ampliamente utilizado en el mejoramiento
de fluidos de perforación. La estabilidad coloidal de los lodos de perforación base de agua
(WBM, por sus siglas en inglés) en presencia de NPs de SiO2 se evaluó mediante el
seguimiento de las propiedades reológicas y de filtración variando el tamaño de partícula,
la concentración y las NP de superficie de carga. Las NPs con el tamaño más pequeño, la
acidez total más alta y el valor más negativo de potencial zeta tuvieron las capacidades
más altas de reducción del volumen de filtración y del espesor del revoque. Estos factores
favorecen las fuerzas de dispersión, permitiendo la reducción de agregados, favoreciendo
Resumen y Abstract X
una deposición ordenada de las partículas logrando una cobertura superior. Una vez
formado el revoque, las fuerzas de atracción predominan en el sistema, reduciendo los
espacios vacíos entre partículas. Además, las NPs se retienen en la superficie porosa
debido a la afinidad entre los grupos de sílice de la roca y los sitios activos de las NPs de
SiO2. Por lo tanto, las NPs de SiO2 podrían interactuar en el siguiente orden con cada
elemento evaluado: Polímero <CaCO3 <Roca. En el caso del polímero, interactúa más con
la roca, seguido de las NP y luego el CaCO3. Las NPs no generan cambios significativos
en los perfiles reológicos del WBM. Sin embargo, el punto de cedencia y la resistencia gel,
que se refuerzan a bajas tasas de cizallamiento, se mejoraron con la presencia de NPs,
las fuerzas de atracción predominan. Cuanto menor sea la distancia entre el polímero y
las NP de SiO2, mayor será la fuerza de atracción entre las moléculas. Este estudio
proporciona un panorama más amplio del rol de las NPs de SiO2 en el mejoramiento de
sus propiedades y el diseño de fluidos de perforación para una aplicación de campo. Se
proponen estrategias y metodologías para la aplicación y escalado del WBM con NPs en
la perforación de pozos.
Palabras clave: Estabilidad Coloidal, Fuerzas entre partículas, Daño de formación,
Fluido de perforación, Filtración, Nanopartícula, Reología, Revoque.
Resumen y Abstract XI
Abstract
SiO2 Nanoparticle to Optimize the Colloidal Suspension Stability and Filter Cake
Buildup in Water-Based Mud
Colloidal suspension agglomeration and filtration occur in many natural phenomena and
engineering applications. The most common colloidal theory problem is stabilizing a
colloidal dispersion. Agglomeration reduction through interparticle force control. If the
particles agglomerate, the agglomerated sizes increase, randomly increasing the
sedimentation (or deposition) rate. Drilling fluids are composed of a base fluid, water, and
solid particles suspended, calcium carbonate - CaCO3.In most cases, polymers are used
to disperse the solid material. However, factors such as mud contamination, size, solid
concentration solids, changes in pH, etc., can alter the surface charge, affect the colloidal
stability, and alter the drilling fluid properties. An alternative to the current improves the
drilling fluids properties is the potential employment of nanoparticle technology. However,
few fundamental studies are available in the literature or omit the interactions between
particles for colloidal suspensions. Thus, the thesis focuses principally on the colloidal
stability in the polymer-CaCO3 system and the solid packing in the filtration process in the
presence of nanoparticles (NPs). SiO2 NPs are a common material widely used in drilling
fluid improvement. The colloidal stability of the water-based drilling muds (WBM) in the
presence of SiO2 NPs was evaluated by monitoring rheological and filtration properties
varying the particle size, concentration, and charge surface NPs. The NPs with the smallest
size, highest total acidity, and the most negative value of zeta potential had the highest
capacities of filtration volume and filter cake thickness reduction. These factors favor the
dispersion forces, allowing the reduction of aggregates, favoring an ordered particle
deposition with superior coverage. Once they have formed the filter cake, the attractive
forces predominate the system, reducing the empty spaces between particles. Also, NPs
are retained in the porous surface due to the affinity between the rock silica groups and the
Resumen y Abstract XII
SiO2 NPs active sites. Hence, the SiO2 NPs could interact in the following order with each
item evaluated: Polymer < CaCO3 < rock. In the case of the polymer, it interacts the most
with the rock, followed by NPs and then CaCO3. NPs do not generate significant changes
in the rheological profiles of the WBM. However, the yield point and gel strength, which are
strengthened at low shear rates, were improved with the presence of NPs, the attractive
forces predominate. The lower the distance between SiO2 NPs-polymer, the greater the
force of attraction between the molecules. This study provides a broader landscape of the
role of SiO2 NPs in the improvement and design of drilling fluids to a field application.
Strategies and methodologies for application and scaling the WBM with NPs in the drilling
are proposed.
Keywords: Colloidal Stability, Interparticle Forces, Drilling fluid, Filter Cake,
Filtration, Nanoparticles, Rheology, Formation Damage.
Content XIII
Content
Pág.
Resumen ............................................................................................................... IX
List of Figures .............................................................................................................. XV
List of Tables ............................................................................................................. XIX
Introduction ............................................................................................................... 22
1. Synthesis, characterization, and preparation of SiO2 NPs and drilling fluid ...... 31 1.1 Experimental .................................................................................................... 32 1.1.1 Materials ........................................................................................................ 32
2. Influence of particle size, surface acidity, and concentration of SiO2 NPs in WBM properties ............................................................................................................... 51
2.1. Experimental .................................................................................................... 52 2.1.1. Materials ........................................................................................................ 52 2.1.2. Methods ......................................................................................................... 52
2.2. Results ............................................................................................................. 52 2.2.1. Rheological parameters ................................................................................. 52 2.2.2. Effect of particle size ...................................................................................... 56 2.2.3. Effect of the surface acidity ............................................................................ 57 2.2.4. Effect of NPs concentration ........................................................................... 62
2.7. Partial conclusions ........................................................................................... 65 2.8. References ....................................................................................................... 66
3. Influence of temperature exposition in WBM properties in the presence of SiO2 NPs ............................................................................................................... 71
3.1. Experimental .................................................................................................... 73 3.1.1. Materials ........................................................................................................ 73 3.1.2. Methods ......................................................................................................... 73 3.1.3. Effect of thermal degradation ......................................................................... 75
3.2. Partial conclusions ........................................................................................... 88 3.3. References ....................................................................................................... 89
4. Effect of SiO2 NPs on external filter cake morphology of colloidal suspensions .. ............................................................................................................... 95
4.1. Experimental .................................................................................................... 96 4.1.1. Material .......................................................................................................... 96 4.1.2. Methods ......................................................................................................... 97
4.2. Results ............................................................................................................. 98
Content XIV
4.2.1. SEM Analysis ................................................................................................ 98 4.2.2. AFM analysis ............................................................................................... 109
4.3. Partial conclusions ..........................................................................................114 4.4. References ......................................................................................................115
5. Effect of colloid filtration in porous media and the subsequent impairment of the rock permeability ......................................................................................................... 119
5.1. Experimental ...................................................................................................120 5.1.1. Material ........................................................................................................ 120 5.1.2. Methods ....................................................................................................... 121
5.2. Results ............................................................................................................123 5.3. Partial conclusion ............................................................................................132 5.4. References ......................................................................................................132
6. Dual effect of SiO2 NPs on the improvement of the mud filtrate: wettability, interfacial tension, and fines migration retention ..................................................... 135
6.1. Experimental ...................................................................................................136 6.1.1. Materials ...................................................................................................... 136 6.1.2. Methods ....................................................................................................... 136
6.2. Results ............................................................................................................138 6.3. Partial conclusions ..........................................................................................142 6.4. References ......................................................................................................143
7. Field application: lessons learned ...................................................................... 147 7.1. Experimental ...................................................................................................147 7.2. Results ........................................................................................................ 153 7.3. Partial conclusions ....................................................................................... 164 7.4. References .................................................................................................. 164
8. Conclusions and recommendations ................................................................... 166 8.1. Conclusions .....................................................................................................166 8.2. Recommendations ..........................................................................................167
9. Publications and awards ..................................................................................... 171 9.1. Scientific papers and book chapter ..................................................................171 9.2. Oral presentations ...........................................................................................172 9.3. Awards ............................................................................................................173
List of Tables XV
List of Figures
Pág.
Figure 1-1: TEM images and the corresponding particle size distribution for (a) Si11, (b)
Si78, (c) Si170, (d) Si11A, (e) Si11B, and (f) SiC NPs. ................................................... 39
Figure 1-2: Zeta potential of synthesized, surface modified, and commercial SiO2 NPs42
Figure 1-3: Functional groups of SiO2 NPs .................................................................... 43
Figure 1-4: FTIR spectrum of the synthesized Si11, Si11A, and Si11B NPs with the
different acidic and basic surface modifications and the commercial SiC NPS. ............... 43
Figure 2-1: WBM viscosity as a function of the shear rate in the absence and presence of
0.1 wt.% of SiO2 NPs at 60 ºC. (a) effect of NPs sizes (b) effect of the acidic and basic
surface. .......................................................................................................................... 54
Figure 2-2: Shear stress of WBMs as a function of the shear rate in the absence and
presence of 0.1 wt.% of different SiO2 NPs at 60 ºC. (a) effect of NPs size (b) effect of the
acidic and basic surface. ................................................................................................ 55
Figure 2-3: Filtration volume obtained as a function of the zeta potential for the WBM in
the presence and absence of 0.1 wt.% SiO2 NPs with different acidic (Si11A) and basic
(Si11B) surface modifications. ........................................................................................ 59
Figure 2-4: SEM photographs (X300-50 µm magnification) of filter cakes obtained in HPHT
filtration for samples a) without NPs and in the presence of 0.1 wt.% of b) Si11, c) Si11B,
and d) Si11A NPs. .......................................................................................................... 60
Figure 2-5: SEM photographs (X30,000-0.5 µm magnification) of filter cakes obtained in
HPHT filtration for samples a) without NPs and in the presence of 0.1 wt.% of b) Si11, c)
Si11B, and d) Si11A NPs. .............................................................................................. 61
Figure 2-6: Mechanism of interaction between SiO2 NPs and polymer/CaCO3 system. . 62
Figure 2-7: Rheological properties of the WBM as a function of the Si11A NPs
concentration: a) PV and YP and b) Gel at 10 seconds and 10 min. ............................... 63
Figure 2-8: Filtration volume as a function of the concentration of Si11A NPs in the
filtration test at HPHT conditions for the WBM at different concentrations (0.01, 0.03, 0.05,
0.1, 0.3, and 0.5 wt.%). ................................................................................................... 65
Figure 3-1: Plastic viscosity (VP) and b) yield point (YP) measured at 77°C of the BFWBM
with and without the synthesized and fumed SiO2 NPs before and after the aging process
at 77°C for 16 h. ............................................................................................................. 76
Figure 3-2: Gel strength measured at 60°C of the WBM with and without the synthesized
and fumed SiO2 NPs a) before (B.R) and b) after (A.R) aging process at 77°C for 16 h. 77
List of Tables XVI
Figure 3-3: Viscosity of drilling fluids as a function of the shear rate in the absence and
presence of 0.1 wt% SiA and SiC NPs at 77 ºC (a) before and (b) after the aging process.
....................................................................................................................................... 78
Figure 3-4: Shear stress of drilling fluids as a function of the shear rate in the absence
and presence of 0.1 wt% SiA and SiC NPs at 77 ºC. (a) before and (b) after the aging
process........................................................................................................................... 79
Figure 3-5: Mechanism of interaction between SiA NPs and xanthan gum molecules.
Polymer chain-breaking after thermal degradation. ........................................................ 82
Figure 3-6: Adsorption isotherms of xanthan gum onto SiA, SiC NPs, and CaCO3 particles
(1000 mg. L-1) obtained varying the initial polymer concentration (100-2500 mg. L-1) and a
fixed temperature of 25°C. .............................................................................................. 86
Figure 3-7: PSD of xanthan gum at 500 mg. L-1 in the presence of SiO2 NPs fresh and
degraded. ....................................................................................................................... 88
Figure 4-1: Overview of the experimental analyses used in this study. .......................... 98
Figure 4-2: SEM photographs (X300-50 µm magnification) of the top surface view of the
filter cake generated by the a) WBM and b) WBM with 0.1 wt.% SiO2 NPs....................100
Figure 4-3: SEM photographs (X55-200 µm magnification) of the cross-section view of
the filter cake generated by the a) WBM and b) WBM with 0.1 wt.% SiO2 NPs. .............101
Figure 4-4: SEM photographs (X200-100 µm magnification) and processed images of two
different zones of the filter cake layer one and the average particle and pore size distribution
(histogram and normal fitting) generated by the filter cake from the a) WBM and b) WBM
with 0.1 wt.% SiO2 NPs. ................................................................................................103
Figure 4-5: SEM photographs (X200-100 µm magnification) and processed images of two
different zones of the filter cake layer two and the average particle and pore size distribution
(histogram and normal fitting) generated by the filter cake from the a) WBM and b) WBM
with 0.1 wt.% SiO2 NPs. ................................................................................................104
Figure 4-6: SEM photographs (X200-100 µm magnification) and processed images of
two different zones of the filter cake layer three and the average particle and pore size
distribution (histogram and normal fitting) generated by the filter cake from the a) WBM and
b) WBM with 0.1 wt.% SiO2 NPs. ...................................................................................105
Figure 4-7: SEM photographs (X200-100 µm magnification) and processed images of two
different zones of the filter cake layer four and the average particle and pore size distribution
(histogram and normal fitting) generated by the filter cake from the a) WBM and b) WBM
with 0.1 wt.% SiO2 NPs. ................................................................................................106
Figure 4-8: The particle size distribution of filter cake layers one to four generated from
the a) WBM and b) WBM with 0.1 wt.% SiO2 NPs. ........................................................107
Figure 4-9: EDS analysis of the filter cake samples generated by the drilling fluids in the
presence and absence of SiO2 NPs for (a) bottom surface and (b) top surface .............108
Figure 4-10: Mechanism of interactions once the solid particle is deposited in the filter cake
surface. .........................................................................................................................109
Figure 4-11: AFM 2D images (topography map) ad their respective 3D images (space
distribution) of three different zones of the bottom view of the filter cake that have SiO2 NPs
concentration of (a) 0.0 wt.%, and (b) 0.1 wt.%. ............................................................111
List of Tables XVII
Figure 4-12: AFM 2D images (topography map) ad their respective 3D images (space
distribution) of three different zones of the top view of the filter cake that have SiO2 NPs
concentration of (a) 0.0 wt.%, and (b) 0.1 wt.%. ............................................................112
Figure 4-13: Average roughness profile for the filter cake generated by the drilling fluids in
the absence and presence of SiO2 NPs at 0.1 wt% of (a) bottom, and (b) top view .......113
Figure 4-14: Schematic illustration of the physical and electrochemical mechanism
between SiO2 NPs-CaCO3 during filter cake formation. .................................................114
Figure 5-1: Experimental set up to damage generation by drilling fluid: 1) the
coreholder, 2) the core, 3) the accumulator cylinders, 4) the high flow pump, 5) the back-
pressure system, 6) the manometer, 7) commercial pump, 8) the collector tank, 9) valves
and 10) drilling fluid [9]. .................................................................................................122
Figure 5-2: Water effective permeability (Kw) as a function of the pore volumes injected
(PVI) for the scenarios without damage and after the exposure of the WBM with and without
0.1 wt.% of SiO2 NPs. ....................................................................................................124
Figure 5-3: Oil effective permeability (Ko) as a function of the pore volumes injected
(PVI) for scenarios without damage, after the exposure of the WBN with and without 0.1
wt.% of SiO2 NPs, and evaluation of Ko return. .............................................................125
Figure 5-4: Cumulative filtration volume as a function of the time during the WBM
circulation over the core face of sandstone core in the presence and absence of 0.1 wt.%
SiO2 NPs. 126
Figure 5-5: Oil relative permeability (Kro) and relative water permeability (Krw) as a
function of the water saturation (Sw) for scenarios 1) without damage, 2) after the exposure
of the drilling fluid without NPs, and (3) WBM with 0.1 wt.% of SiO2 NPs. .....................128
Figure 5-6: Oil recovery factor (%OOIP) as a function of the pore volumes injected
(PVI) for the scenarios after the exposure of the drilling fluid:1) without NPs, and 2) with 0.1
wt.% of SiO2 NPs. ..........................................................................................................129
Figure 5-7: Viscosity of the crude oil effluents for the scenarios at a fixed shear rate of
100 s-1: 1) after the exposure of the drilling fluid with and without 0.1 wt.% of SiO2 NPs and
2) during the evaluation of Ko return, and 3) at different control point; 3, 6, and 9 PVI...130
Figure 5-8: Mechanism of interactions of the NPs-polymer system with porous media .131
Figure 6-1: Experimental setup to perform the fines retention experiments [32]. .........137
Figure 6-2: Contact angles for the water/air/rock system treated with the mud filtrate: a)
without NPs and b) with 0.1 wt.% SiC for 0 and 20 seconds. .........................................138
Figure 6-3: Spontaneous imbibition curves for sandstone cores soak with mud filtrate in
the absence and presence of 0.1 wt.%. SiO2 NPs. ........................................................140
Figure 6-4: The breakthrough curve for the sand samples treated with mud filtrate in the
absence and the presence of SiO2 NPs. ........................................................................141
Figure 6-5: Mechanisms of interactions of NPs once they enter the porous media through
mud filtrate. ...................................................................................................................142
Figure 7-1: Removal section and tank arrangement for preparation and circulation of the
WBM with and without NPs ...........................................................................................152
Figure 7-2: Photographic record of the filter cake (HPHT test) after thermal degradation: a)
WBM without NPs and b) WBM with 0.05 wt.% NP1. ....................................................154
List of Tables XVIII
Figure 7-3: Photographic record of the filter cake (HPHT) after heat treatment: a) WBM
without NP1, b) WBM with 0.05 wt.% NP1/carrier fluid, and c) WBM with 0.05 wt.%
NP1/water .....................................................................................................................156
Figure 7-4: Photographic record of the filter cake (PPT) after heat treatment: a) WBM
without NP1 and b) WBM with 0.05 wt.% NP1/water .....................................................157
Figure 7-5: Invasion profile for the: a) Wells A and b) Well B. .......................................160
Figure 7-6: Barrels of fluid per day (BFPD), basic sediment and water (BSW), barrel of oil
per day (BOPD), frequency of electric downhole pump (ESP), and pressure intake pump
(PIP) for the: a) Wells A and b) Well B. ..........................................................................162
Figure 7-7: Actual BFPD, BOPD, BSW, and PI for Wells A and B (13/02/2021). ..........162
List of Tables XIX
List of Tables
Pág.
Table 1-1: Additives and composition of WBM ............................................................. 34
Table 1-2: Median hydrodynamic diameters (d50), total acidity (NH3 uptake), and surface
area (SBET) of the synthesized and commercial SiO2 NPs with different sizes and surface
modification. ................................................................................................................... 38
Table 1-3: WBM properties ............................................................................................ 44
Table 2-1: The yield point (𝜏𝑜), plastic viscosity (𝜇𝑝), flow consistency index (𝐾), flow
behavior index (𝑛) treated as Bingham-plastic and Herschel–Buckley models for all the
WBMs that contain 0.1 wt.% SiO2 NPs at 60 ºC. ............................................................ 55
Table 2-2: Volume filtration (𝑉𝑓), filter cake thickness (ℎ𝑚𝑐), and filter cake permeability
(𝐾𝑚𝑐) calculated from Darcy's Law of the filter cake and respective reduction of the filtration
test obtained under HPHT conditions for all the WBMs that contain 0.1 wt.% SiO2 NPs. 57
Table 3-1: The yield point, plastic viscosity, flow consistency index, flow behavior index,
mean squared error, and the root mean square error treated as Bingham-plastic and
Herschel–Bulkley models the WBM contain 0.1 wt% SiA and SiC NPs at 60 ºC. ............ 80
Table 3-2: Filtration volume, mudcake thickness, and mudcake permeability calculated
from Darcy's Law of the mudcake and respective reduction of the filtration test obtained
under HPHT conditions WBM in the presence and absence of 0.1 wt.% SiA and SiC NPs.
....................................................................................................................................... 83
Table 3-3: Spurt loss, filtration volume at 30 min, and total filtration volume of the filtration
test obtained under HPHT conditions of the WBM in the presence and absence of 0.1 wt.%
SiA and SiC NPs. ........................................................................................................... 84
Table 3-4: Estimated SLE model parameters for polymer adsorption onto SiA, SiC NPs,
and CaCO3 particles (1000 mg. L-1) obtained varying the initial polymer concentration (100-
2000 mg. L-1) and a fixed temperature of 25°C. .............................................................. 86
Table 3-5: Mean aggregate size of xanthan gum at 500 mg. L-1 in the presence of SiO2 NPs
fresh and degraded. ....................................................................................................... 88
Table 4-1: Filter cake layer properties from image processing analysis .......................107
Table 4-2: The properties of fresh fouled, physical cleaning, and chemical cleaning
membranes ...................................................................................................................113
Table 5-1: Properties of the cores used in the displacement tests. ............................121
List of Tables XX
Table 5-2: Summary parameters obtained during the displacement tests: Swr, Sor, and
their respective reduction percentages. .........................................................................129
Table 7-1: Drilling fluid formulation for the field application............................................148
Table 7-2: Wellbore diagram and drilling fluids..............................................................150
Table 7-3: Drilling conditions during interval C7. ...........................................................151
Table 7-4: HPHT filtration for the WBM before and after heat treatment varying the NP1
concentration. ................................................................................................................153
Table 7-5: HPHT filtration for the WBM before and after heat treatment: a) WBM without
NP1, b) WBM with 0.05 wt.% NP1/carrier fluid, and c) WBM with 0.05 wt.% NP1/water.
......................................................................................................................................155
Table 7-6: PPT filtration for the WBM before and after heat treatment: a) WBM without NP1
and b) WBM with 0.05 wt.% NP1/water. ........................................................................157
Table 7-7: Rheological properties before and after heat treatment: a) WBM without NP1,
b) WBM with 0.05 wt.% NP1, and c) WBM with 0.05 wt.% NP1/water. ..........................158
Table 7-8: Summary of the WBM properties evaluated in the field for the initial,
homogenized, and final stages. .....................................................................................159
Table 7-9: Petrophysical properties for Well A and B through well log analysis. ............161
Table 7-10: Solid content Well A and B during production. ...........................................163
List of Tables XXI
Introduction
Colloidal suspension flow and filtration in porous media have become very relevant for
different applications, such as water treatment [1, 2], remediation of clays [3, 4], food
processing treatment [5-7], coating and painting [8-10], oil enhanced recovery and well
injectivity [11-13], and drilling operations [11, 14, 15]. The most common colloidal theory
problem is comprehending the colloidal suspension stability involving physical and
chemical properties, making it difficult to understand. The term colloidal stability refers to
the dispersion of colloids in the fluid [16]. If the agglomerate particles, the aggregates
increase their sedimentation, generating disorganized and low-packed sediment. The
colloidal stability is significant to control: (i) the rheological properties of dispersion and (ii)
define the quality of the filter bed.
Colloids are typically defined with a diameter ranging from 1 nm to 1000 nm dispersed in a
fluid [5, 17]. Colloids have a Brownian, hydrodynamic, and interparticle motion to overcome
gravity and remain suspended. Colloidal stability depends on several types of interactions:
Van der Walls and electrostatic interactions (classical Derjaguin-Landau-Verwey-Overbeek
theory - DLVO) [18] and steric interactions [19]. Electrostatic interactions are purely
attractive, repulsive, or both. The Van der Waals attractive interactions cause particle
aggregation; the London dispersion interacts with particles to cause attraction (induced
dipoles) [16]. The electrostatic stabilization mechanism is due to repulsive forces; the
particle surface is charged, having ionic groups physically adsorbed or chemically attached
to the surface [16]. The surface groups can be positively or negatively charge, developing
an electrical double layer. The superposition of the layers around two charged particles
leads to repulsion [17]. In the steric stabilization mechanism, surfactant or polymer
molecules are adsorbed onto particle surfaces, giving repulsive steric forces. When two-
particle polymers overlap, a repulsive force is generated due to osmotic pressure and
elastic components [20]. The polymer saturation in the overlap region induces an increase
Introduction 23
in the local osmotic pressure due to the disparity in concentrations between polymer and
solvent. The second factor corresponds to elastic stabilization. Compressing polymers
limits their degrees of freedom, and this reduction in configurational entropy increases free
energy. The system is not thermodynamically favorable, the particles tends to be separated
[21]. These mechanisms are used in concentrated colloidal suspension.
As the particles, collide and agglomerate, agglomerates with larger diameters can form.
Once the diameter exceeds the colloidal size limit or external factors such as pressure,
temperature, others exceed their Brownian motion; it is impossible to control how they are
deposited. Various factors that affect the colloidal stability in the electrostatic mechanism
can be the pH or the ionic strength of the media, ion type and concentration, zeta potential
value (related with the pH), and size particle [16]. Regarding steric mechanism, aggregation
could occur where non-adsorbing polymers in solution induce depletion forces [8, 22].
Finally, the external factor can alter colloid stability, chemicals, heat, salt, and desorption.
Depending on the stability degree, the particles are aggregated and deposited due to
gravitational forces in the porous media. The interaction between particles and rock can
occur by several mechanisms: attachment, straining, size exclusion, bridging, etc. [23-25].
Once the particle is deposited is subjected to hydrodynamic forces such as drag, permeate,
lift, buoyancy, and electrostatic forces. Electrostatic and penetration forces allow particles
to adhere to the surface, while drag, lift, and gravitational forces constantly erode the retort
surface [11, 14, 26]. In this way, the colloidal suspension stability, the way particles are
deposited (aggregate size), and the hydrodynamic forces that act on the previously
deposited particle define the effectiveness of the filtration process.
The base fluid could charge the solid particle surfaces in the drilling fluid, contributing to an
electrostatic repulsion mechanism. Regularly, solid particles have different sizes and
concentrations, micron-size ranges. Polymers help the suspension of the solid particles
during pipeline trips. This compound is located between the solid-liquid interface and
generates an electrostatic barrier that delays or prevents particle collisions, making the fluid
more stable. Different additives are present in drilling fluid that mix or disperse to have a
stable colloidal suspension. However, the importance of the colloidal phenomenon in the
drilling fluid has been overestimated. A stable colloidal solution, applied to drilling fluids,
consists of fine solid particles that are not deposited by a protective film, generally protective
Introduction 24
colloids or electrolytic action or both, exhibiting a desired viscosity, weight, and filtration
control. The viscosity property allows the transport and release of the cuts to the surface.
The filtration control enables forming a seal on the well face with the retention of solid
particles in the surface [27].
Water-based muds (WBM) are widely used, 90% of the cases. The formulation of polymer
and calcium carbonate (CaCO3)-based fluids has been growing as it is less abrasive, can
replace barite as densifying agents, and is soluble in acid [28-30]. Other types of additives
are incorporated to provide specific characteristics to minimize or control negative impacts
during drilling. One of the key strategies in the design of WBM is the effective formation of
a low-permeable filter cake. The CaCO3 particle size has been optimized [30, 31], polymers
have been used as filtration control additives and viscosifying agents [32, 33], and other
additives such as dispersing agents that favor the formation of the filter cake [34]. However,
when the particles are not small enough, the fluid is contaminated, the pH is altered, and
the suspension does not exhibit the necessary stability. The particles can flocculate and
sediment rapidly due to the attractive Van der Waals forces between particles. Once the
aggregates are deposited on the wellbore wall, a render with high roughness, thickness,
permeability, and porosity is obtained that allows the flow of filtrate through the formation
[15, 35]. In this way, nanoparticles (NPs) are presented as an alternative to improve the
drilling fluids design.
Most authors have used NPs in bentonite-based drilling fluids (BWBM), even knowing the
limitation of these drilling fluids and the formation damage generated, to reduce the filter
cake filtration volume and thickness [36]. Authors have investigated the effect of the nature
or type of NPs [37-41], the size and shape [39, 42], the surface modifications [39, 43, 44],
and the presence of agents that alter the NPs surface charges [42]. Most NPs employed
have been the hybrid NPs-clay based on Fe2O3 and Al2O3-SiO2 [27]; Fe2O3 and SiO2 NPs
[49] and SiO2 NPs impregnated with cellulose [50]. The most important results lie in the
NPs evaluation had been zeta potential. NPs NPs with the highest negative zeta potential
values favor NPs dispersion and alter the surface charges of clays (bentonite), promoting
repulsion due to the negative charges located at the edges of the clays, generating a net
negative charge. Electrostatic repulsion prevents coagulation, clattering and subsequently
favors forming a more robust structural network between the clays improving the rheological
and filtration parameters. Some authors have developed NPs, microparticles, and fibers
impregnated with cellulose [45] and SiO2 NPs modifications since synthesis or
Introduction 25
impregnations with polymers [44, 46]. The studies above did not consider the colloidal
stability of the drilling fluid in the presence of NPs and the subsequent filtration behavior.
Recently, the use of CaCO3 has been extended for the drilling industry, but few studies
involve the use of NPs in WBM based CaCO3 and polymers. Contreras et al. [47]
synthesized two types of NPs: (1) iron-based (Np1) and (2) calcium-based (Np2). The
authors evaluated the effect of NP1 and Np2 at concentrations of 0.5 to 2.5 wt.% for filtration
control and reduction of formation damage. Srivatsa et al. [48] have been a few authors
who have evaluated SiO2 NPs as a substitute for CaCO3 in WBM. However, it is not to
consider the colloidal stability phenomena due to the addition of NPs in WBM based CaCO3
and polymers. Additionally, few studies show that NPs can reduce the filtration volume and
improve the filter cake structure due to the electrostatic forces between components.
Hence, this thesis aims to understand the fundamentals of filtration kinetics, which is usually
coupled with Brownian motion and with particle aggregation due to the colloidal stability
suspension in the polymer-CaCO3 system in the presence of NPs. Water-based drilling
fluids based on CaCO3 and polymer denoted in the thesis as WBM and silica NPs (SiO2
NPs) were chosen among the drilling fluid with minor formation damage and the NPs most
used to improve the drilling fluid performance. Further, the specific objectives are:
I. Synthesized and characterize silica-based NPs.
II. Identify the different types of interactions in the NPs/CaCO3 and NPs/Polymer
systems.
III. Estimate the effect of pH, surface charge, and NPs concentration on the colloidal
suspension stability and solids packing.
IV. Propose different phenomenological mechanisms for improving the solid packing
morphology and subsequent filtration volume reduction.
V. Evaluate the effect of colloidal filtration in porous media and the subsequent
impairment of the rock permeability through the coreflooding test.
VI. Define strategies and methodologies for applying and scaling a WBM with NPs
in the drilling of a well.
Hence, this document is divided into seven main chapters that include: 1) Synthesis,
characterization, and preparation of SiO2 NPs and drilling fluid, 2) Influence of particle size,
surface acidity, and concentration of SiO2 NPs in WBM properties, 3) Effect of SiO2 NPS
Introduction 26
on external filter cake morphology, 4) Dual effect of SiO2 NPs on the improvement of the
mud filtrate: wettability and IFT changes and fines retention, 5) Inhibition of the drilling-
induced formation damage by WBM under dynamic conditions, and 6) Field application:
Lessons learned.
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Introduction 28
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Introduction 29
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Introduction 30
1. Synthesis, characterization, and preparation of SiO2 NPs and drilling fluid
Nanotechnology has gained significant importance in applying the oil and gas industry in
different areas, such as formation damage [1, 2] and enhancing oil recovery [3].
Nanoparticles (NPs) modify reservoir properties, such as wettability, improve mobility
between formation fluids, and even control solid particles flow through porous media due
to NPs size between 1 and 100 nm [3]. The nanometric size provides a high surface
area/volume ratio that favors the mass and energy transfer phenomena [3]. Consequently,
the drilling industry has been no exception. NPs have improved the properties of the drilling
fluid such as the thermal and electrical conductivity [4, 5], the rheological properties of the
drilling fluid [6-10], avoiding well instability, especially in shale areas [11, 12], reducing
friction during drilling [13, 14], and decreasing the filtration volume by obtaining a better-
quality filter cake [15-20]. The last being the one with the highest number of studies
reported. For instance, some authors had evaluated different chemical nature of NPs [21-
24], intercalated clay hybrid [8, 25], nano-polymer material [6, 7, 26], and other oxide metal
NPs such as SiO2, Fe2O3, ZnO, CuO NPs and carbon nanotubes [4, 9, 27, 28]. Recently,
the SiO2 Nps have great attention due to their stability, low toxicity, and ability to be
functionalized with a range of molecules [29-31]. In this order, this chapter describes the
synthesis and characterization of synthesized SiO2 NPs through the sol-gel method (e.g.,
Stöber silica) and the high-temperature pyrolysis routes (e.g., fumed silica). Finally, NPs
were characterized by trough particle size, zeta potential, chemical composition, surface
acidity, and surface area.
Otherwise, bentonite is one of the most employed additives in water-based mud (WBM)
due to its low costs and physicochemical properties that provide adequate rheology and
filtration characteristics [32, 33]. However, bentonite may suffer degradation, hydration, and
breaking [34], leading to flocculation and low drilling fluid performance [35]. Sized calcium
carbonate (CaCO3) has recently been implemented in drilling fluids for being less abrasive
and more stable under high-temperature conditions [36, 37]. Instead, a WBM based on
Chapter 1 32
CaCO3 and polymers was used to evaluate the effect of the SiO2 NPs. Additionally, the
basic, rheological, and filtration properties were assessed as the reference of this study,
baseline.
1.1 Experimental
1.1.1 Materials
Ethanol as co-solvent (99.9%, Panreac, Spain), ammonium hydroxide used as a catalyst
(NH4OH, 28%, J.T. Baker, USA), and tetraethyl orthosilicate as the precursor of silica
(TEOS >99%, Sigma Aldrich, USA) were used to synthesize the SiO2 NPs. For the surface
modification of the NPs, HCl (37%, Sigma Aldrich, USA) and NaOH (>98%, Sigma Aldrich,
USA) were used. The commercial NPs of fumed SiO2 (SiC NPs) were obtained from Sigma-
Aldrich (99%, St. Louis, MO).
The WBM employed in this study has a conventional composition of a drilling fluid widely
implemented in the drilling of Colombian wells: water, xanthan gum as a viscosifying
polymer (Sigma Aldrich, USA), sodium carboxymethylcellulose (PAC, Sigma Aldrich, USA),
and starch (C6H10O5)n, Sigma Aldrich, USA) used as a filtration control additives and, 600,
325, and 1200 mesh calcium carbonate used to densifying and a bridging material in drill-
in fluids (CaCO3, Minercol, Colombia), and its pH was adjusted with NaOH to maintain the
fluid in pH alkalinity (>98%, Sigma Aldrich, USA).
1.1.2 SiO2 NPs synthesis
The synthesis of three SiO2 NPs was done following the sol-gel method using TEOS as a
silica precursor based on the method proposed by Stöber [1, 2]. The mixture was prepared
in a beaker following TEOS, ethanol, deionized water, and ammonia. The solution must be
continuously mixed for five hours at 25°C and dried on a stove for 24 hours at 120°C [38].
To obtain SiO2 NPs, the general TEOS:H2O:NH4OH:ethanol molar ration used was
0.9:1:0.2:1.1. To get different sizes of SiO2 NPs, the TEOS:H2O molar ratio was varied in
0.9: 1, 0.7: 1, and 0.5:1.
Chapter 1 33
• NPs functionalization
The surface modification of NPs was performed using acidic and basic solutions. For this,
200 mL of an aqueous solution of 0.3% of HCl or NaOH were prepared to obtain pH values
of 3 and 10, respectively. Posteriorly, an amount of 0.5 g of NPs was submerged in each
solution for 24 hours and then sonicated for two hours at 25°C. Finally, the NPs were
separated by centrifugation, washed with deionized water, and dried at 120 °C for six hours
[38]. The nomenclature of NPs was established according to the chemical nature (silica,
Si), size, and surface modification, e.g., Si11A denotes SiO2 NPs of 11 nm treated with an
acidic solution [3].
1.1.3 SiO2 NPs characterization
• NPs size
The mean diameter size (d50) and morphology of the SiO2 NPs were measured using
dynamic light scattering technique (DLS) and transmission electron microscopy (TEM). For
the DLS measurement, a small amount of the NPs were dispersed in a 5 ml aqueous phase
using sonication and then introduced to a zetasizer analyzer (NanoPlus-3, Micromeritics
Instrument Corp. GA) at room temperature with the help of a glass cell. To evaluate the
morphology Transmission Electron Microscopy (TEM). For TEM measurements, the NPs
were dispersed in ethanol and deposited on a TEM lacey carbon grid. The analysis was
performed on a Tecnai F20 Super Twin TMP microscope (FEI, USA) with a resolution of
0.1 nm, operated at 200 kV as accelerating voltage.
• Compositional evaluation
Fourier transformed infrared (FTIR) (IRAffininty-1s spectrophotometer, Shimadzu, Japan)
was used to characterize the functional groups at the surface of the SiO2 NPs. About 300
mg of KBr pellets (background spectrum) was added to the 13 mg NPs sample, and the
spectra were recorded in a range from 4500 to 500 cm-1 [39-41].
• Zeta potential
A specific dry mass (50 mg) of the synthesized and fumaric NPs must be added to 50 ml of
deionized water. The initial solution was divided into ten samples, and the pH varied
between 2 and 12, adding drops of NaOH or HCl in a constant magnetic mixing.
Subsequently, the NanoPlus 3 was used for the zeta potential value, where an electric field
is applied to a dispersion of NPs in water.
Chapter 1 34
• Programmed Desorption (TPD) of ammonia (NH3)
The TPD of the NH3 technique was used to measure the total acidity of synthesized and
fumaric NPs. A ChemBet TPR/TPD (Quantachrome Instruments, USA) was used. The
amount of NH3 desorbed is an indication of the total acidity of the NPs studied.
Approximately 100 mg of the sample should be introduced into a U-shaped quartz
microreactor. The sample was dried at 200°C for 1 hour under helio (He) flow at
atmospheric pressure to remove adsorbed water and other gases. Subsequently, the
sample was brought to 100°C, and the He flow was switched to NH3. NH3 is adsorbed onto
the sample surface at 100°C for 1 hour at atmospheric pressure. Then, the physisorbed
NH3 is removed with the He flow over the solid for 1 hour at 100°C. Subsequently, the
sample was heated to 900°C at a rate of 10°C.min-1 for the desorption of the previously
adsorbed NH3. The amount of NH3 desorbed as a temperature function is calculated based
on the area under the peak using a calibration curve [38].
• Surface area (SBET)
SBET of NPs was determined using the Brunauer-Emmett-Teller (BET) method [42]. For
this, nitrogen adsorption-desorption is carried out at -196 ° C using an Autosorb 1
equipment from Quantachrome (United States). Samples were degassed at 140 ° C under
the dynamic vacuum of 10-6 mbar. Surface areas were calculated using the BET equation
[42].
1.1.4 Drilling fluid preparation
The WBM was prepared by mixing each additive for ten minutes in the mixer (Hamilton
Beach, USA) at low speed in the order mentioned in Table 1-1. The NPs were added in
concentrations of 0.1 wt.% according to previous studies [43] after the xanthan gum
hydration.
Table 1-1: Additives and composition of WBM
Additive Function Composition
Deionized water Base liquid 340 ml
Caustic soda (NaOH) Alkalinity agent The required until the pH is
adjusted (9.5 pH - 10pH)
Xanthan Gum Viscosifying agent 0.5 g
Chapter 1 35
Additive Function Composition
Polyanionic cellulose Fluid loss control 4.5 g
Pre-gelatinized starch Fluid loss control 4.0 g
Calcium carbonate 1200
Weighting and bridging
material
4.5 g
Calcium carbonate 600 17.5 g
Calcium carbonate 325 8.5 g
Calcium carbonate 200 5.0 g
Laboratory formula to prepare the equivalent of 1 barrel (1 Bbl)
1.1.5 Drilling fluid characterization
The drilling fluids were characterized by the determination of the density, pH, and solids
content. The density was estimated using a mud balance (Fann, Texas, USA) and a
pressurized mud balance (Fann, Texas, USA) to obtain density values closer to those
obtained at the bottom of the well. For the pH measurement, a digital pH meter was used
(Oakton, USA). The solid content was carried out through retort analyses using a sample
of 10 mL (Fann, Texas, USA). All protocols are based on the API 13B-1 standard norm [44].
• Rheological properties of drilling fluids
WBM rheological properties were measured using a rotational viscometer model 35 (Fann,
Texas, USA), varying the velocity from 3 to 600 rpm at a temperature of 60°C. Each
experimental condition set was repeated three times. Plastic viscosity (PV) and yield point
(YP) were determined as follows:
𝑃𝑉 = 𝜃600 − 𝜃300 (1.1)
𝑌𝑃 = 𝜃300 − 𝑃𝑉 (1.2)
where, 𝑃𝑉 is the plastic viscosity (cP), 𝜃600 and 𝜃300 are the Fann values at 600 and 300
rpm, and 𝑌𝑃 is the yield point (lbf/100 ft2). The gel strength (Gel) at 10 seconds, 10 minutes,
and 30 minutes was also estimated and corresponded to the maximum dial reading at the
respective time [44].
Many rheological models have been developed to fit shear stress and shear rate for
Newtonian and no-Newtonian fluids [45]. The Bingham-plastic model (BP) is the easiest to
use due to its linear behavior [46]. However, for complex fluids, the relationship between
Chapter 1 36
shear stress and shear rate is non-linear. The Herschel−Bulkley model (HB) is commonly
used in drilling fluids where the main components are solids [6, 47]. The BP and HB models
are expressed in Eq. 3 and 4, respectively. The experimental data obtained varying the
velocity from 3 to 600 rpm, equivalent to 5 to 1021 s-1 using the conventional factor 1.7023
from RPM to s-1, was fitted with the rheological model discussed before.
𝜏 = 𝜏0 + 𝜇𝑝�� (1.3)
𝜏 = 𝜏0 + 𝐾��𝑛 (1.4)
where 𝜏 is the shear stress (lbf/100 ft2), 𝜏0 is the yield stress (lbf/100 ft2), 𝜇𝑝 is the plastic
viscosity (cP), �� is the shear rate (s-1), 𝐾 is the consistency index (lbf.sn/100ft2), and 𝑛 is the
flow behavior index (dimensionless).
• High-Pressure High-Temperature (HPHT) filtration test
An HPHT Filter Press (Fann, Texas, USA) was used to register the filtration volume under
static pressure and temperature of 500 psi and 60 ºC following a standard procedure [44].
The filter cake thickness was measured using a digital caliper (700-113 MyCal Lite,
Mitutoyo America Corp, USA) with several repetitions. The obtained filter cake was dried at
120 °C and characterized by scanning electron microscopy (SEM) (JEOL, JSM-6490LV,
Japan). Finally, the permeability of the filter cake was calculated applying Darcy’s Law as
follows [32]:
𝐾𝑚𝑐 = 40.93𝑞∙𝜇𝑓∙ℎ𝑚𝑐
𝐴∙∆𝑃 (1.5)
where, 𝐾𝑚𝑐 (µ𝐷) is the permeability of the filter cake, 𝜇𝑓 (cP) is the mud filtrate viscosity, 𝑞
(𝑚𝐿 𝑠⁄ ) is the filtration rate; ℎ𝑚𝑐 (mm) is the filter cake thickness, 𝐴 (𝑐𝑚2) is the area, and
∆𝑃 (psi) is the pressure drop across the filter cake.
1.2 Results
1.2.1 Particle size, SBET, and acid surface
The mean particle size (d50), the surface acidity, and the SBET are summarized in Table 1-2
for the synthesized and fumed SiO2 NPs. Different synthesized SiO2 NPs with a particle
size of 11, 78 y 170 nm were obtained by modifying the TEOS/H2O ratio, showing that d50
Chapter 1 37
increases as this ratio decreases, which agrees with the reported by Betancur et al. [38].
The sizes of the S11, S78, and S170 NPs increase with decreases in the TEOS/H2O ratio
as the TEOS:H2O ratio increases, the amount of available water decreases, and the
hydrolysis reaction rate decreases, which decreases the probability of the addition of a
monomer to the network, resulting in smaller particle size. Hence, the NPs were terminology
according to the particle size as Si11, Si78, and Si170 NPs. After the surface modification
process described above, the acid surface treatment (Si11A) and basic surface treatment
(Si11B) showed d50 of 11.3 and 61.9 nm. Si11B presented a d50 increment; it could be
related to more functional groups adsorbed onto NPs surfaces. According to the synthesis
method, SiC showed the smallest d50 among the synthesized NPs with 7.0 nm; the closest
was the Si11 NPs. Fumed silica is synthesized by the pyrolysis method, in which silicon
tetrachloride reacts with oxygen in a flame, followed by rapid quenching to room
temperature. This process controls the size of NPs. The sol-gel method is performed in a
liquid phase, and silica NPs were synthesized with an acidic or basic catalyst and alcoholic
solvent in the presence of silicon alkoxide precursor [48]. For the last method, the variables
can be controlled to modify the size and morphology. The size of the surface-modified NPs
could be related to the surface modification process, which is related to the interactions of
the NPs surface and the solvent employed for dispersion or the length of the chemical
groups impregned in the surface [38]. The size of the NPs was evaluated through DLS in
aqueous solutions to obtain a more realistic condition regarding the based fluid in the WBM.
Additionally, this condition can determine the nanofluid in the porous media, considering
the ratio of particle size/pore throat size and its possible obstruction [49, 50]. Figure 1-1
depicts a TEM photograph of the SiO2 NPs and the particle size distribution obtained by
TEM image analysis. Mainly amorphous SiO2 NPs appeared in the photograph with no
sharp edges independent of the synthesis method, where the d50 of NPs is very close to
the DLS estimated. Also, the larger particle size appearing in TEM images was attributed
to particle aggregation of the NPs.
As expected, the SBET increased with a decrease in particle size; the SBET follows the order
Si170<Si78<Si11, as the same volume was divided into smaller parts, the surface area
increases non-linearly. NPs that possess a high surface area with a small diameter react at
a higher react rate. The surface-modified NPs, Si11A and Si11B, showed a similar and
increment of the SBET, respectively. The basic surface modification could be related to the
increment of the particle size. According to the synthesized method, the SiC NPs showed
Chapter 1 38
the higher SBET, similar to the particle size. The Si11A showed the higher total acidity related
to NH3 adsorbed by each NPs [51]. It can be noticed that superficial acid treatments were
effective. The treatment with the HCl to these samples enhanced the surface acidity,
creating Brönsted and Lewis acid sites [52] preferentially. Lewis acidity could be explained
by the presence of siloxane bridge sites (Si–O–Si), formed by the dehydroxylation of the
silica surface due to the acid treatment, while the weak Brönsted acid sites related with the
silanol groups (Si-OH) (see Figure 1-3). These silica groups can donate or receive protons,
especially H+, and alter the charge from the HCl (H+ and Cl-). The total surface acidity of
the three synthesized NPs (Si11, Si78, and Si170), even the fumed silica NPs were lower
than SiA NPs values, is due to no changes in the chemical structure. These NPs presented
-OH groups from the silanol groups, whereas the SiA NPs could offer H+ additional onto the
surface.
Table 1-2: Median hydrodynamic diameters (d50), total acidity (NH3 uptake), and surface area (SBET) of the synthesized and commercial SiO2 NPs with different sizes and surface modification.
NPs d50 (nm) NH3 uptake
(mmol.g-1) SBET (m2.g-1) ± 1.0
Si11 11.3 ± 0.1 1.57 ± 0.2 213
Si78 78.0 ± 0.7 1.50 ± 0.2 140
Si170 170.2 ± 1.4 1.48 ± 0.4 13
Si11A 11.2 ± 0.2 1.76 ± 0.5 213
Si11B 61.9 ± 2.4 1.59 ± 0.2 165
SiC 7.0 ± 0.3 1.43 ± 0.8 278
Chapter 1 39
Figure 1-1: TEM images and the corresponding particle size distribution for (a) Si11, (b) Si78, (c) Si170, (d) Si11A, (e) Si11B, and (f) SiC NPs.
b)
a)
c)
Chapter 1 40
e)
d)
f)
Chapter 1 41
1.2.2 Zeta potential
Zeta potential is the electric potential at the slipping plane relative to a point in the bulk
medium. Zeta potential is often considered as the effective charge on the particle [52].
Figure 1-2 shows the zeta potential as a function of the pH for the synthesized NPs with
different surface acidity and the fumaric NPs. The point at which zero electrophoretic
mobility occurs is called an isoelectric point. If a more basic solution is added, then the
particles tend to acquire a more negative charge. Dissociation of acidic groups onto NPs
surface will give rise to a negatively charged surface. Protonation or deprotonation of
silanols in the presence of H3O+ or OH- [53]. Zeta potential analysis is a technique for
determining the dispersion stability of NPs in solution. At a pH of 10, the zeta potential of
the synthesized and fumaric SiO2 NPs reached values lower than -30 mV, being the lowest
for the Si11A material, which could indicate the degree of electrostatic repulsion between
adjacent, similarly charged particles in a dispersion [10]. The Si11A NPs, due to the
acidification process, showed the highest total acidity compared with the other synthesized
or fumaric samples. The Si-OH groups can be easily functionalized with adequate
reactants. The functionalization modifies the support surface charge and hydrophilic
character [54]. The H+ and OH- in solution from the acidic and basic treatments,
respectively, can interact with the negative and positive poles from the silanol group, which
gives to the material acidic and basic properties, cationic or anionic behavior, this through
physisorption processes by intermolecular forces [38, 55]. Zeta potential becomes more
negative due to progressive protonation of Si-OH groups [54] (SiOH ↔SiO- + H+,
Si(OH)Si↔SiO-Si+H+, and SiOH+OH-↔Si(OH)2-) [56]. Although the SiC NPs could present
higher Si-OH groups on their surface (high SBET), the protonation of this group is lower than
the synthesized NPs treat with HCl.
Chapter 1 42
Figure 1-2: Zeta potential of synthesized, surface modified, and commercial SiO2 NPs
1.2.3 FTIR
Figure 1-4 shown a qualitative evaluation of the surface modification of the NPs following
the functional groups of interest. The surface chemical composition of SiO2 NPs is based
on siloxane (Si–O–Si) and silanol groups (SiOH). There are different types of silanol groups:
isolated silanols ( Si-OH), geminal silanols ( Si(OH)2), and vicinal or H-bonded silanols
( Si(OH) –O– (OH)Si ), as shown in Figure 1-3. All NPs (synthesized and fumaric)
showed the same bands, with a slight change in transmittance intensity. The band between
3500 y 3600 cm -1 can be related to the vibrations of the free –OH- groups stretching and
bending on the surface [57]. The –OH- bond, related to water, generates an extensive band
for the SiC NPs due to the high SBET. The 1200 cm-1 and 826 cm-1 bands were related to
the Si-OH stretching Si-O-Si symmetric stretching [58, 59]. The band at 698 cm-1 was
assigned to Si–O–Si asymmetric stretching and the peak at 1600 cm-1 to –OH- groups of
the absorbed water molecules or overlapping of Si–OH groups. Furthermore, an exposure
of the Si-OH bonds at 1200 cm-1 was observed, looking at the difference spectrum between
synthesized and fumaric materials. This band is situated in the fingerprint region; the –OH-
groups are present in the NPs structure (or skeleton). Generally, these functional groups
modified the NPs surface charge, anionic character, corroborated for the zeta potential that
increases for the modified NPs and favoring the dispersion between the particles. The
difference spectrum between SiA and SiC materials can be attributed to the greater
presence of –OH- groups due to the synthesis. However, as the FTIR spectra correspond
Chapter 1 43
to bulk measurements, it is not enough for determining the tested nanomaterial surface
activity. However, Montes et al. [60] evaluated through XP spectra to identifying the surface
chemical nature. Authors defined that the silanol on the surface of the nanomaterials has
the trend fumaric > synthesized. These results corroborate the high presence of –OH-
groups on SiC NPs surface.
Figure 1-3: Functional groups of SiO2 NPs
Figure 1-4: FTIR spectrum of the synthesized Si11, Si11A, and Si11B NPs with the different acidic and basic surface modifications and the commercial SiC NPS.
Chapter 1 44
1.2.4 Drilling fluid properties
The WBM properties are presented in
Table 1-3, in which it can be observed that the WBM density was 9.0 ppg. These values
are consistent with the drilling fluid components evaluated. Additionally, it was observed
that the pH is basic. Otherwise, the HPHT filtration and rheological properties are presented
as a reference for the study.
Table 1-3: WBM properties
PROPERTIES VALUE
Density (ppg) 8.9
Pressurized mud balance (lb/gal) 9.0
pH 10.2
Total solids (%V/V) 2
𝑽𝒇 HPHT (ml en 30 min) 16.4
𝒉𝒎𝒄 HPHT (mm) 1.69
VP (cP) 36
YP (lb.100ft-2) 25
Gel (lb.100ft-2) (10 s/ 10 m/ 30 m) 4 / 5 / 5
1.3 Partial conclusions
SIO2 NPs was successfully synthesized through the sol-gel method. NPs were
characterized by particle size, zeta potential, chemical composition, surface acidity, and
SBET measurements. Also, commercial NPs were characterized. SiO2 NPs resulted in the
nanometric range and decreased d50 trend as the amount of precursor increased. Also, the
amorphous shape and diameter size were corroborated through TEM images. As expected,
the surface area increased with a decrease in particle size. The trend followed by the zeta
potential of the synthesized SiO2 NPs was Si11<Si11B<Si11A. SiC NPs presented similar
values to the unmodified NPs (Si11). The surface modification process onto SiO2 NPs of
11 nm showed a considerable reduction in surface acidity in Si11B samples. Meanwhile,
Chapter 1 45
the value for the Si11A material is similar to the Si11 NPs. The Si–OH groups can be easily
functionalized with adequate reactants. The effect of functionalization is modifying the
surface charge and hydrophilic character of the support. Finally, the basic, rheological, and
filtration properties were evaluated as the reference of this study, baseline.
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Chapter 1 46
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Chapter 1 48
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Chapter 1 49
2. Influence of particle size, surface acidity, and concentration of SiO2 NPs in WBM properties
When two colloidal particles dispersed in a fluid are close together, the van der Waals and
repulsion forces act on each other. The sum of each interaction indicates the total and
predominant interaction force in the system [1]. Such behavior can define particle adhesion
to surfaces, particle separation during dispersion, particle aggregation and deposition rates,
and rheology estimation.
The predominant interaction mechanism in a system, attraction or repulsion, depends on
certain factors [2]. Attraction decrease with increasing distance between particles; when
the concentration of particles in a dispersion increases and the average separation distance
between particles decreases, the attractive forces increase [3]. For particles with large radii,
the attraction often dominates. The dispersion medium, water, pH, salt content; modify the
zeta potential [3, 4]. The particle could increase or decrease the negative or positive ions
or the particle. Generally, the negative charge generates repulsion. Similar solid particles
are always repulsive, but they can be attractive between dissimilar chemical particles [5].
However, in complex fluids, it can be challenging to define the predominant interaction
energy in the face of combinations of several factors.
Colloids immersed in an aqueous fluid coexist in a WBM. With the polymer aid, particle
dispersion is promoted to improve the drilling fluid viscosity and filtration. Additionally, NPs
have an essential role in reducing the drilling fluid filtration and filter cake thickness due
they could favor the dispersion between solid particles [6, 7]. NPs restructured mode of
solid particles interact attributed to a modification in surface charge as demonstrated by
zeta potential measurements [6]. However, no studies evaluate the influence of particle
size, surface acidity, and concentration of SiO2 NPs in reducing filtration volume and the
filter cake thickness in the specialized literature. Their surface charge, surface area, and
Chapter 2 52
properties could alter the electrostatic forces and the interactions between drilling fluids
components. Therefore, this chapter will focus on suspension stability and subsequent
change in the WBM properties as rheology and filtration control. We will see how NPs
factors such as particle size, zeta potential, and concentration alter the colloidal stability.
We will study this by considering the interaction between the representative NPs in the
system and the interaction between the different WBM components.
2.1. Experimental
2.1.1. Materials
Refer to Table 1-1 and Table 1-2 in Chapter 1 with details on the NPs characteristics and
drilling fluid composition.
2.1.2. Methods
The size, acid surface, and concentration of SiO2 NPs effect were evaluated by analyzing
the rheological and HPHT filtration properties following the procedure described in Section
1.1.5. Then, the best chemical nature of NPs was used to analyze the effect of NPs
concentration on the WBM properties according to methods exposed in section 1.1.5.
2.2. Results
2.2.1. Rheological parameters
The basic properties of the WBM in the absence and presence of 0.1 wt.% of SiO2 NPs
with different sizes and surface modifications were determined. The addition of NPs did not
alter the density of the WBM with values of 8.9 ± 0.1 lb.gal-1 for all samples, which indicates
that the well stability would not be affected, avoiding the natural fractures formation or an
undesired influx during drilling [8]. The NPs addition did not alter the pH values, reducing
the probability of particles flocculation that affects the WBM properties. The solids content
was 2.0 ± 0.1wt.% and can be classified as low-solid WBMs, according to Caenn et al. [9].
The PV values did not present representative changes, 17 cP, for all samples. Also, NPs
addition did not alter the YP with 9 lbf.100 ft-2. Only the Si11A NPs showed an increase of
YP by 33% with a value of 12 lbf.100ft-2, which could increase the suspension capacity of
Chapter 2 53
the rock cuts during drilling [10]. The increment in the rheological parameter, especially
viscosity, indicates the formation of a more robust gel structure. Polymer mobility and self-
diffusion induced rearrangement of the polymer; network structures were formed through
the polymer chains connecting particle clusters. This behavior is due to an interaction of
silanol and siloxane groups onto NPs surface (-OH groups) and the polymer structure (-
COOH groups) through hydrogen bonding. Finally, adding different particle sizes of SiO2
NPs did not alter the Gel behavior at 10s/ 10m/ 30m of the WBM.
Figure 2-1 shows the viscosity of the WBM in the presence and absence of SiO2 NPs of
different sizes (Figure 2-1.a) and acidity surface (Figure 2-1.b). The WBM has a shear-
thinning behavior over the entire range of shear rate, viscosity decrease when the shear
rate increase. High viscosity is obtained at low shear rate values (< 200 s-1) and favors the
particle suspension during stop circulation. At high shear rates (> 200 s-1), the viscosity was
reduced to allow the circulation of the fluid [11]. Xanthan gum is a high molecular anionic
polysaccharide that exhibits shear-thinning behavior, attributed to the uncoiling and partial
alignment of the XG chains at the high shear rate region [12]. WBM in the presence of NPs
with different sizes did not alter the viscosity, revealing that the interaction between NPs
and the viscosifying agent was not determinant. However, the Si78 NPs slightly reduced
the viscosity at low shear rates, as shown in Figure 2-1.a. NPs with different surface acidity
did not show a significant alteration in viscosity, mainly at high shear rates, as can be seen
in Figure 2-1.b. However, Si11B NPs presented a slight reduction at high shear rates.
Availability of hydrogen bonding sites depends on the particle size (surface area), surface
acidity, concentration, among other factors. However, the size and acidity effect are not
significant enough to generate a noticeable change in viscosity, at least at the concentration
evaluated. It is proposed as a possible hypothesis that the NPs of smaller size (greater
surface area) and surface acidity present a more significant amount of -OH groups that can
interact with the polymer. In the presence of Si11A NPs, repulsion forces between like
charges along the XG backbone (e.g., the negative charges on the COO- functional groups)
stretch and elongate the chains. A lower NPs concentration of this type (Si11A NPs) could
be required to achieve changes in viscosity, the opposite of larger NPs or those of a neutral
and basic character.
Chapter 2 54
Figure 2-1: WBM viscosity as a function of the shear rate in the absence and presence of 0.1 wt.% of SiO2 NPs at 60 ºC. (a) effect of NPs sizes (b) effect of the acidic and basic surface.
The effect of the selected NPs at a fixed dosage of 0.1 wt.% at 60 ºC in the shear stress is
shown in Figure 2-2. Figure 2-2.a. show that the NPs size did not show a significant
influence in the shear stress regarding the WBM in the absence of NPs. Nevertheless, the
Si11A NPs, Figure 2-2.b., caused an upward shift of the rheogram up to +16% for shear
rates between 100 and 200 s-1 than the WBM without NPs, is necessary a more significant
force acting to cause deformation. The acidic surface of the NPs can build a microstructure
due to the stronger attractive forces, which increase the resistance of polymers to move
when shear stress is applied and improved the wellbore cleaning efficiency [13]. Under low
shear rates, the attractive forces are predominant, and the distance between particles is
reduced, so the interaction between NPs/WBM components could increase. The separation
distance is assumed to be the maximum distance between particles suspended; the
repulsive forces are predominant, and the polymer chains alienation is presented at high
shear rates [14]. According to the studies developed by Olivera et al., SIO2 NPs formed
clusters around the polymer chains [15]. NPs delayed the helix to coil conformation
transitional structure transition [16]. For the acid surface NPs, Si11A NPs, the H+ ions that
predominate in the acid surface become ionized at high pH (10), causing the NPs-polymer
attraction through hydrogen bonding. The charged surfaces also decrease particle
aggregation.
Chapter 2 55
Figure 2-2: Shear stress of WBMs as a function of the shear rate in the absence and presence of 0.1 wt.% of different SiO2 NPs at 60 ºC. (a) effect of NPs size (b) effect of the acidic and basic surface.
The Bingham Plastic (BP) and Herschel−Bulkley (HB) models fitted to the experimental
data are shown in Table 2-1. The HB model had the best fit according to the values of the
statistical parameters, including the correlation coefficient (R2), with values > 0.99, and the
root mean square error (RMSE), close to 1 %. The flow consistency index (𝐾) showed an
increase around ± 55%, and the flow behavior index (𝑛) exhibited a low reduction of ± 7%
by the addition of the SiO2 NPs regardless of the particle size or chemical nature of the
surface. The term 𝐾 is defined as the fluid consistency index and describes the thickness
of the drilling fluid. The flow behavior index 𝑛 indicate the degree of non-Newtonian. An
increase in 𝐾 leads to higher the viscosity and carrying capacity of WBM, hence, to better
bottom hole cleaning and more drilling efficiency [17]. Low values of 𝑛 indicate that the
WBM has lower viscosity at high shear rates to favor penetration. Additionally, when 𝑛 is
low, a lower loss of pressure in regions of high shear rate occurs, e.g., WBM inside the drill
pipe and in the bit nozzles. Therefore, smaller 𝑛 means greater hydraulic efficiency [18].
Table 2-1: The yield point (𝜏𝑜), plastic viscosity (𝜇𝑝), flow consistency index (𝐾), flow
behavior index (𝑛) treated as Bingham-plastic and Herschel–Buckley models for all the
WBMs that contain 0.1 wt.% SiO2 NPs at 60 ºC.
Model WBM Si11 Si78 Si170 Si11A Si11B
BP 𝝉𝒐 (𝒍𝒃 𝟏𝟎𝟎 𝒇𝒕𝟐⁄ ) 3.46 3.10 2.31 8.94 3.38 2.31
𝝁𝒑 (𝒄𝑷) 0.05 0.05 0.05 0.37 0.06 0.06
Chapter 2 56
𝑹𝟐 0.9861 0.9857 0.9783 0.9820 0.9784 0.9783
𝑹𝑴𝑺𝑬 0.115 0.193 0.144 0.120 0.130 0.144
HB
𝝉𝒐 (𝒍𝒃 𝟏𝟎𝟎 𝒇𝒕𝟐⁄ ) 2.46 0.20 0.92 1.91 2.00 0.92
𝑲 (𝒍𝒃 𝟏𝟎𝟎 𝒇𝒕𝟐𝒔𝒏 ⁄ ) 0.28 0.41 0.44 0.45 0.43 0.44
𝒏 0.72 0.67 0.67 0.61 0.68 0.67
𝑹𝟐 0.9991 0.9813 0.9990 0.9976 0.9996 0.9990
𝑹𝑴𝑺𝑬 0.038 0.128 0.038 0.246 0.024 0.038
SiO2 NPs-xanthan gum interaction could be done through hydrogen bonding between the
silanol and the carboxylate groups [16]. Such interaction had been reported to increase the
polymer thermal stability with little impact on the rheological properties (see chapter 3).
Generally, NPs may work as points between the polymer chains, which support the
strengthening of the viscoelastic structure of the WBM [12, 19]. Based on molecular
dynamic simulation results, evaluating the radius of gyration (ROG) of the polymer, the
effect of the NPs addition on the apparent viscosity suggests a minor impact of the ROG of
xanthan gum in the presence of the NPs [20]. This finding helped us to corroborate the
experimental observations of Figure 2-1 and Figure 2-2. More details about SiO2 NPs effect
in rheological properties are discussed in chapter 3.
2.2.2. Effect of particle size
Table 2-2 shows the filtration volume (𝑉𝑓), filter cake thickness (ℎ𝑚𝑐), and filter cake
permeability (𝐾mc), obtained in the HPHT filtration test of the WBM in the presence and
absence of 0.1 wt.% SiO2 NPs of different sizes, 11, 78, and 170 nm, at 500 psi and 60ºC.
The Si11 NPs exhibited the lowest mud filtrate and filter cake thickness compared with the
WBM in the absence of NPs, reducing 19 and 20%, respectively. Meanwhile, for the Si78
and Si170 NPs, the filtration volume reduction was 8 and 12%, respectively. Additionally,
Si78 and Si170 NPs reduced filter cake thickness by around 10% for both materials. In
terms of filter cake permeability, Si11, Si78, and Si170 were decreased by 35, 18, and 24%
compared with the base mud. The NPs size had several effects under filtration volume and
filter cake thickness; size affects the dispersion stability; smaller sizes present more
excellent dispersion and could avoid the aggregation between particles and themselves
[21]. Also, this behavior occurs due to the surface area increment due to the NPs size
Chapter 2 57
reduction, which means that there was more area to interact with the fluids and particles.
The surface chemistry of the SiO2 NPs is made of two types of sites: the hydrophobic
siloxanes Si-O-Si and the hydrophilic silanols Si-OH. In contact with water, silica surfaces
typically expose Si–O–Si and Si-OH groups. The deprotonation of Si–O–Si and Si-OH
groups renders the surface negatively charged SiOSi+ HOH↔SiOH and SiOH+ HOH↔SiO-
+H+. NPs could attain electrical charges by absorbing water molecules and forming a
hydration layer when dispersed in water. Hydration effects become more evident with high
surface area or high content of siloxane groups, which allows a higher concentration of ions
and improves the repulsion [4]. Additionally, the smallest NPs can enter and stay in the
space not occupied by the micrometric material particles reducing the filter cake porosity
and permeability. According to the results, Si11 NPs were selected for the surface
modification to obtain acidic and basic-modified NPs and improve their surface charge [22].
Table 2-2: Volume filtration (𝑉𝑓), filter cake thickness (ℎ𝑚𝑐), and filter cake permeability
(𝐾𝑚𝑐) calculated from Darcy's Law of the filter cake and respective reduction of the filtration
test obtained under HPHT conditions for all the WBMs that contain 0.1 wt.% SiO2 NPs.
Material 𝑽𝒇 (ml) Change in
𝑽𝒇 (%) 𝒉𝒎𝒄 (mm)
Change in
𝒉𝒎𝒄 (%) 𝑲𝒎𝒄 (uD)
Change in
𝑲𝒎𝒄 (%)
WBM 20.0 ± 0.1 - 1.69 ± 0.07 - 0.14 ± 0.02 -
Si11 16.2 ± 0.1 -19 1.35 ± 0.60 -20 0.11 ± 0.05 -35
Si78 18.4 ± 0.1 -8 1.51 ± 0.74 -10 0.12 ± 0.01 -18
Si180 17.6 ± 0.3 -12 1.53 ± 0.93 -9 0.13 ± 0.04 -24
Si11A 12.8 ± 0.2 -36 0.58 ± 0.65 - 66 0.07 ± 0.03 - 59
Si11B 15.6 ± 0.1 -22 1.24 ± 0.33 - 27 0.13 ± 0.05 - 24
2.2.3. Effect of the surface acidity
Based on the results obtained in the size effect, the NPs with the best performance were
Si11 NPs. Hence, this section has been used for evaluating the impact of the surface acidity
under HPHT filtration measurements. As observed in Table 2-2, the higher the reduction of
𝑉𝑓, ℎ𝑚𝑐, and 𝐾𝑚𝑐 was obtained for the system with Si11A NPs with values of 36, 66, and
59%, respectively. The best performance of the Si11A NPs can be related to the most
Chapter 2 58
negative zeta potential values (surface charge density) [5], and the highest surface acidity
values among all materials evaluated, leading to higher repulsion forces, see section 1.2.2.
The anionic behavior of Si11A NPs promotes the electrostatic repulsive forces caused by
the negative charge surface attributable to the silanol and hydroxyl groups. Also, the CaCO3
negative charges observed under alkaline conditions could promote this repulsion [7]. The
acidity surface modification increased the H+ groups due to the surface modification with
HCl. Ions H+ y OH- could interact with the silanol o siloxane group and increase the
electronegative charge. Regarding the basic treatment with NaOH, ions OH- y Na+ cover
the surface groups reducing the electronegative charge. Additionally, the SiO2 NPs in the
WBM act as loss material additives to reduce the filtration volume due to their nanometric
size. NPs could enter into the space that does not occupy the micrometric CaCO3 and
improve the pore plugging [23].
Further, it can be said that the NPs can occupy the spaces between the bridging material,
favoring the repulsion and the stability of the WBM [23]. A relationship between the filtration
volume and the NPs zeta potential can be obtained, as shown in Figure 2-3. Lower filtration
volume for the lowest zeta potential value confirms the dispersion forces influence.
Reduction of the WBM filtrate due to the higher stability of the NPs for values higher than -
30 mV. The results agreed with the studies of Mahmoud et al. [24] and Parizad et al. [22].
They studied the zeta potential effect in the filtration reduction relating to the negative
charge of the SiO2 NPs in bentonite-based drilling fluids (BWBM). The zeta potential of the
WBM without NPs corresponds to the CaCO3 at 60 ºC and pH = 10.
Chapter 2 59
Figure 2-3: Filtration volume obtained as a function of the zeta potential for the WBM in the presence and absence of 0.1 wt.% SiO2 NPs with different acidic (Si11A) and basic (Si11B) surface modifications.
Filter cake obtained in each HPHT filtration test during the evaluation of the acidic surface
effect of the SiO2 NPs was characterized through SEM analysis to provide a better
understanding of the phenomena on the filter cake microstructure. SEM photographs of the
WBM in the a) absence of NPs and the presence of b) Si11, c) Si11B, and Si11A NPs
analyzed by SEM are shown in Figure 2-4. As observed in Figure 2-4 .a, the filter cake
without NPs showed larger pore space and the large size of CaCO3 aggregates, which
allowed a higher filtrate flow. The inclusion of NPs modified the filter cake morphology,
decreasing porosity. The aggregate size of the CaCO3 was reduced in the order Si11 <
Si11B < Si11A as the zeta potential decreased. The filter cake with Si11A NPs presented
a more homogeneous morphology and the smallest aggregate size of the CaCO3 particles
leading to lower porosity. Nps favor the dispersion of the CaCO3 in suspension, avoiding
aggregation. Once the action of pressure deposits the particles, there is coverage of and
ordering the particles on the surface (see Figure 2-6). More details about filter cake
morphology in the presence of SiO2 are shown in Chapter 4.
Chapter 2 60
Figure 2-4: SEM photographs (X300-50 µm magnification) of filter cakes obtained in HPHT filtration for samples a) without NPs and in the presence of 0.1 wt.% of b) Si11, c) Si11B, and d) Si11A NPs.
Figure 2-5 shows the SEM images at ×30000 of the obtained filter cakes in the absence
and presence of the NPs. Si11A NPs (Figure 2-5.d) interacted with the polymers building a
barrier that covers the particles, decreasing the porosity as a crosslinking effect. The
phenomena could occur for synergy in the SiO2 NPs-polymer system. Silanol groups on the
surface of the SiO2 NPs can interact through hydrogen bonding with the carboxylic groups
(-COOH) of the polymers used in this WBM, as has been reported by Kennedy et al. [16]
and Giraldo et al. [25]. This coverage on CaCO3 reduced the space between particles,
decreasing the filter cake porosity and permeability and consequently the filtration volume
(see Figure 2-6). More details about SiO2 NPs-polymer interaction are shown in chapter 3.
Chapter 2 61
Figure 2-5: SEM photographs (X30,000-0.5 µm magnification) of filter cakes obtained in HPHT filtration for samples a) without NPs and in the presence of 0.1 wt.% of b) Si11, c) Si11B, and d) Si11A NPs.
Covering
a)
No NPs
b)
Si11
c)
Si11B
d)
Si11A
Chapter 2 62
Figure 2-6: Mechanism of interaction between SiO2 NPs and polymer/CaCO3 system.
2.2.4. Effect of NPs concentration
Figure 2-7 show the NPs concentration effect in the PV, YP, and Gel of the WBM. As
expected, PV increases as the NPs concentration in the system increase. Increasing the
concentration of the solid particles decreases the space between particles; therefore, the
attractive forces become predominant in the system. Once the NPs interact with the
polymer, the attractive forces between NPS-polymer molecules increase, strengthening
friction and increasing viscosity [26]. Si11A NPs had a stronger interaction with the polymer.
A viscous base fluid causes high PV, which means altering the crosslinking effect [27].
Regarding the YP, this presents the same behavior as the PV values. NPs increase the YP
values as the concentration increase. However, the effect was more robust in the YP than
the PV after the addition of NPs. The average increment for the PV was 13%, hence YP.
The average increment was observed by 20% compared with the WBM without NPs. The
YP is considered the flow resistance due to the fluid electrochemical forces under dynamic
conditions [28]. These electrochemical forces (attractive forces) were improved due to the
SiO2 NPs-polymer interactions due to the adsorption process [6, 29, 30].
Chapter 2 63
For the concentration range between 0.01 wt.% and 0.1 wt.%, the gel strength presented a
slight increase, although, at higher concentrations, the properties increase around 54%
concerning the WBM without NPs. The Gel is a significant rheological property that
indicates building a gel structure during static conditions and suspends the solids and
cuttings [11, 28]. SiO2 NPs presented better electrostatic forces (attractive forces) under
static conditions than under dynamic. The repulsion forces predominant the system under
dynamic conditions, but the aggregation is principal under static conditions. It suggests that
the static conditions of the fluids favor the Si11A NPs-polymer interactions than dynamic
conditions. NPs could improve the rheological parameter of the drilling fluids through
different mechanisms that depend on the continuous phase, water, mud system, and NPs
characteristics, as shown in previous researchers [6, 19, 31-35]. NPs dispersed in the WBM
could increase the friction between layers, increasing viscosity [16, 25, 31]. The NPs and
polymer may be linked together through specific chemical linkages to increase the PV, YP,
and Gel. When SiO2 NPs concentration increases, the viscosity of the drilling fluid increases
because the adsorption of the particle surface is not limited or enough, hence promoting
the NPs-polymer bridging interaction. This interaction promotes the repulsion between
polymer chains.
Figure 2-7: Rheological properties of the WBM as a function of the Si11A NPs concentration: a) PV and YP and b) Gel at 10 seconds and 10 min.
Chapter 2 64
Figure 2-8 shows the filtration volume of the HPHT filtration test at 0.03, 0.05, 0.1, and 0.3,
wt.% of Si11A NPs. As expected, the 0.1 wt.% concentration of Si11A NPs, presented the
highest percentage of filtration reduction by 22%; this is the optimal point for this evaluated
concentration. However, concentrations greater than 0.1 wt.% of NPs showed adverse
effects in reducing the filtration volume, indicating that NPs could be aggregate and
precipitate or reduce the dispersion effect themselves. Once optimum concentration was
exceeded, a negative impact on filtration properties was observed. The aggregation
between particles reduces the distance between them, so the Van der Waals forces are
representative.
Chapter 2 65
Figure 2-8: Filtration volume as a function of the concentration of Si11A NPs in the filtration test at HPHT conditions for the WBM at different concentrations (0.01, 0.03, 0.05, 0.1, 0.3, and 0.5 wt.%).
The drilling fluid has two states, the suspension of particles when the drilling fluid is in
circulation and the formation of a cake due to the pressure differential or the cessation of
fluid circulation. The interaction forces on the particles in each situation are the same, but
the magnitude is different. In suspension, the particles are relatively far apart, even more
so when there is fluid circulation, which causes the repulsive forces between particles to
predominate in the system. Once the filter cake has formed, the distance between particles
is significantly reduced, favoring the attractive forces. In this way, the colloidal suspension
stability and the reduction of the size of the aggregate are favored. Hence, the attraction of
the particles was increased by reducing the filter cake porosity. This behavior is consistent
with DLVO, where the distance between particles defines the electrostatic forces that
predominate in the system.
2.7. Partial conclusions
HPHT filtration test was carried out for SiO2 NPs of different sizes, surface acidity, and zeta
potential. The NPs with the smallest d50, highest total acidity, and the most negative value
of zeta potential had the highest capacities of filtration volume and filter cake thickness
reduction. These factors favor the dispersion forces, allowing the removal of aggregates,
favoring an ordered particle deposition with superior coverage. Once they have formed the
Chapter 2 66
filter cake, the attractive forces predominate the system, reducing the empty spaces
between particles.
The addition of NPs does not generate significant changes in the rheological profiles of the
WBM. However, the rheological properties such as YP and Gel, which are strengthened at
low shear rates, improve with the presence of NPs, the attractive forces predominate. The
viscoelastic structure of the fluid was enhanced. The lower the distance between SiO2 NPs-
polymer, the greater the force of attraction between the molecules.
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[30] J. V. Clavijo, L. J. Roldán, L. Valencia, S. H. Lopera, R. D. Zabala, J. C. Cárdenas, et al., "Influence of size and surface acidity of silica nanoparticles on inhibition of the formation damage by bentonite-free water-based drilling fluids. Part I: nanofluid design based on fluid-nanoparticle interaction," Advances in Natural Sciences: Nanoscience and Nanotechnology, vol. 10, p. 045020, 2019.
[31] A. R. Ismail, N. M. Rashid, M. Z. Jaafar, W. R. W. Sulaiman, and N. A. Buang, "Effect of nanomaterial on the rheology of drilling fluids," Journal of applied sciences, vol. 14, p. 1192, 2014.
[32] Y. Jung, Y.-H. Son, J.-K. Lee, T. X. Phuoc, Y. Soong, and M. K. Chyu, "Rheological Behavior of Clay–Nanoparticle Hybrid-Added Bentonite Suspensions: Specific Role of Hybrid Additives on the Gelation of Clay-Based Fluids," ACS applied materials & interfaces, vol. 3, pp. 3515-3522, 2011.
[33] M.-C. Li, Q. Wu, K. Song, Y. Qing, and Y. Wu, "Cellulose nanoparticles as modifiers for rheology and fluid loss in bentonite water-based fluids," ACS applied materials & interfaces, vol. 7, pp. 5006-5016, 2015.
[34] S. R. Smith, R. Rafati, A. Sharifi Haddad, A. Cooper, and H. Hamidi, "Application of aluminium oxide nanoparticles to enhance rheological and filtration properties of water based muds at HPHT conditions," Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 537, pp. 361-371, 2018.
[35] Z. Vryzas, L. Nalbandian, V. T. Zaspalis, and V. C. Kelessidis, "How different nanoparticles affect the rheological properties of aqueous Wyoming sodium bentonite suspensions," Journal of Petroleum Science and Engineering, vol. 173, pp. 941-954, 2019.
Chapter 2 69
3. Influence of temperature exposition in WBM properties in the presence of SiO2 NPs
Drilling fluids in practice contain polymers. These may be adsorbed to the particles,
chemically attached to the surfaces, or they may be free in solution [1]. Polymers in colloidal
suspensions allow the stabilization of the particles from steric stabilization. The adsorbed
polymers make a strong repulsion between particles that must be added; Van der Waals
attractions are minimized [1, 2]. Polymer adsorption onto particle surface produces a layer
that can be charged by the molecules of the polar solvent, water, in the case of the WBM.
The gelling structures in the drilling fluid increase the viscosity and contribute to the stability
of the solid particles. In this way, the particles will be deposited in an orderly manner [3].
However, when colloidal stability in drilling fluid is broken down by chemical, mechanical,
and electrical means, the fluid can lose its rheological and filtration properties. Polymers
molecules based on carbon chains suffer breaks at high temperatures or pressure [4].
Drilling fluids must operate for long periods at dynamic circulation and pressure conditions;
with increasing depth, the temperature increases. These conditions are unfavorable to the
WBM rheological and filtration properties. Polymers could suffer degradation due to
hydrolysis, depolymerization, or other chemical degradation through two mechanisms. One
is the random breaking of the bonds, and the other is a chain-breaking in the C-C bonds
[4]. Lower-molecular weight or deflocculation causes a viscosity and filtration control
reduction [5-7]. To overcome these problems, many researchers in the drilling industry have
developed higher temperature resistance polymer adding organic compounds [8], heat
resistant synthesized polymer [9-12], and modifying the common polymers [13, 14].
Although the authors had been made to increase the polymer temperature limitation, it
could not solve the problem due to high costs; these continue to be polymers that suffer
degradation [15, 16].
Chapter 3 72
Hence it requires the addition of non-polymeric additives such as NPs, which are more
stable at high temperatures (>700 °C in air conditions) [15]. Agarwal et al. [17] replaced
polymeric surfactants with hydrophobic nanosilica and organically modified nanoclay to
stabilize oil-based muds. After the thermal rolling process, the NPs preserved emulsion
stability, and the water droplet was conserved. Although the YP was slightly reduced by
23%, the VP was increased by 15%. Mahmoud et al. [18] aged a WBM with 0.5 wt% Fe2O3
and SiO2 NPs at 200ºC. The authors demonstrated that the drilling fluid with Fe2O3 NPs
resulted in minor changes in the yield stress (YS) increased by 42%, while SiO2 NPs
presented the highest percentages by 130%. Hence, the VP increase by 166 and 211%
for the Fe2O3 and SiO2 NPs, respectively. Parizad et al. [19] evaluated the effect of TiO2
NPs in a WBM with 10 wt.% of KCl after thermal degradation. Drilling fluid was reduced by
17% of its PV and 30% of YP. The addition of 0.75 wt%. of TiO2 NPs presented an excellent
resistance in this regard and reduced PV and YP by 8% and 15%, respectively. The filtration
volume with TiO2 NPs was 5% against 12% of the drilling fluid without NPs. Perween et al.
[20] synthesized ZnTiO3 NPs through the Sol-gel method (SNP NPs) and electrospinning
technique (ENP NPs) and evaluated the effect varying the concentration from 0.5 wt% to 3
wt%. They analyzed the NPs addition on the WBM rheological and filtration properties with
xanthan gum and PAC as the main polymers before and after thermal degradation. ENP
NPs presented a more pronounced impact on rheological and filtration properties. After the
thermal aging process, API filtration volume of base mud was reduced by 33% and 35.86%
using 3.0% (w/v) NPs concentrations of SNP and ENP, respectively. Base drilling fluid
reduced the apparent viscosity (AV) by 17.3% after rolling. However, this decrease in PV
was 6% by adding SNP at 3.0% (w/v) and 12% for ENP at the same concentration.
Based on the literature exposed above, no studies evaluate the influence of SiO2 NPs
improving the rheological and filtration properties after temperature exposition. There is no
phenomenological insight about the SiO2 NPs-polymer interaction and the effect on
colloidal stability. Also, it is intended to evaluate two routes of processes for NPs obtention
for medium and large-scale production forms with a view to a field application. In this way,
the starting point is the Si11A NPs according to the results above, from now denoted SiA,
and fumed silica NPs, SiC. This chapter aims to evaluate the effect of the SiC and SiA NPs
on inhibiting polymer degradation, consequently improving the rheological and HPHT
filtration properties in WBM colloidal stability. Finally, the WBM gravity stability and bridging
Chapter 3 73
properties were evaluated through filtration control using the permeability plugging tester
(PPT). The SiO2 NPs-polymer interaction was analyzed through adsorption studies and
aggregate size behavior.
3.1. Experimental
3.1.1. Materials
Detailed information about NPs and WBM employed can be found in Chapter 1.
3.1.2. Methods
The effect of temperature exposition in WBM properties in the presence of SiO2 NPs was
evaluated through rheological properties analysis following the procedure described in
section 1.1.5. before and after thermal degradation (process described below). According
to the results of section 2.2., the best optimal concentration of SiO2 NPs was used to
analyze the thermal stability of the WBM according to the filtration properties considering
the HPHT filtration test (section 1.1.5) and pore plugging test (describe following). The NPs-
polymer and CaCO3-polymer interactions were evaluating through adsorptions isotherms
and the aggregate behavior through the DLS technique.
• Pore plugging tester (PPT).
Drilling fluids were evaluated in the PPT (OFITE, United States) using a ceramic disk with
a mean pore throat of 20 um (OFITE, United States). The filtration cell was loaded with a
volume of 300 mL of drilling fluid and heated to 77°C with the pressurized system at 100
psi. Upon reaching the test temperature, the cell was pressurized to 1100 psi to maintain a
delta pressure of 1000 psi. Once the pressure of interest was obtained, 30 seconds were
counted from the opening, and the filtration volume was measured corresponding to the
spurt loss. Finally, the filtration volume is quantified every 10 minutes, and the total volume
is reported at 30 min. The total filtration volume (𝑉𝑇) was calculated as follows:
𝑉𝑇 = 𝑉𝑠 + (2 ∗ 𝑉30) (3.1)
where, 𝑉𝑠 is the spurt loss (mL) and 𝑉30 is the filtration volume at 30 min (mL).
Chapter 3 74
• Aging Process
All drilling fluid samples were thermally degraded using a roller oven (OFITE, United States)
at 77 °C for 16 h. After aging, the basic, rheological, and filtration properties were
determined using the same procedure for the fresh drilling fluids.
• Polymers adsorption test
The adsorption tests were performed in batch–mode experiments by fixing the amount of
SiO2 NPs and CaCO3 of 0.1 wt% (1000 mg. L-1) and varying the concentration of polymer
(100 to 2500 mg. L-1) according to the procedure described by Guzman et al. [21] at 25°C.
Initially, in the drilling operations, the polymers are hydrated. Subsequently, the other
additives were added; this procedure was replicated in the laboratory. The NPs were
incorporated after the hydration of xanthan gum. Hence, the same route was followed by
the addition of the materials to the adsorption process. The polymer was stirred and
stabilized according to the procedure discussed above. After that, the materials were added
and stirred slowly for 48 h, a time necessary for reaching the adsorption thermodynamic
equilibrium and guarantee the adsorbate-adsorbent interaction [21]. First, the adsorbed
polymer materials were separated from the solution by centrifugation for 2 h at 4500 rpm
using a centrifuge (Z306 Hermle Universal Centrifuge, Labnet, United States) and dried at
atmospheric conditions. The amount adsorbed (𝑁𝑎𝑑𝑠) was determined by mass balance
using TGA under air atmosphere with a temperature ramp from 20 to 800°C at a fixed
heating rate of 20°C.min-1 and airflow of 100 mL. min-1.
• Adsorption Isotherms.
Some different types of adsorption isotherms have been reported in the literature, e.g.,
Langmuir [22], Freundlich [23], Solid-Liquid equilibrium model (SLE) [24, 25], among others.
According to the study by Giraldo et al. [26], Langmuir and Freundlich's model provides
limited insight on the adsorption mechanism between polymer and NPs. The authors
founded that RMSE% values were greater than 10%. Therefore, the present study
employed the SLE model to describe the interactions between polymer - NPs that have
been reported successfully by Giraldo et al. [26] with RMS<10%.
Solid-Liquid equilibrium model. This adsorption isotherm model describes the behavior
of self-associative molecules onto a solid surface and is expressed as follows:
Chapter 3 75
𝐶𝐸 =𝜓𝐻
1+𝐾𝜓𝑒𝑥𝑝 (
𝜓
𝑁𝑎𝑑𝑠,𝑚) (3.2)
Where, 𝐻 (mg. g-1) is Henry's law constant, related to the adsorption affinity, the strength of
polymer interactions onto the NPs. Higher Henry parameter, the higher the affinity; K (g. g-
1) is an indicator of the polymer self-association once the primary sites are occupied. 𝑁𝑎𝑑𝑠,𝑚
(mg. g-1) are the maximum adsorption capacity of NPs (mg. g-1). The other parameters are
defined as follows:
𝜓 =−1+√1+4𝐾𝜉
2𝐾 (3.3)
𝜉 =𝑁𝑎𝑑𝑠,𝑚∗𝑁𝑎𝑑𝑠
𝑁𝑎𝑑𝑠,𝑚−𝑁𝑎𝑑𝑠 (3.4)
• Aggregate behavior of the SiO2 NPs-polymer system.
The mean aggregate size of the polymer can change by the addition of SiO2 NPs.
Measurements were carried out through the DLS technique at 25 °C for a xanthan gum
solution at a fixed concentration of 500 mg. L-1 (representative concentration of WBM) and
with the addition of 0.1 wt.% SiA and SiC NPs before and after thermal degradation. The
polymer samples were heated at 77 °C for 16 h. The hydrodynamic diameter of the
aggregate (polymer and polymer with NPs) was measured. More details about particle size
evaluation can be found in section 1.1.3.
3.1.3. Effect of thermal degradation
• Rheological properties
Figure 3-1 shows the PV and YP for the WBM in the absence and presence of 0.1 wt.% of
SiA and SiC NPs before and after thermal degradation. PV was increased by 11 and 13%
due to 0.1 wt% SiA and SiC NPs, respectively, for the fresh drilling fluid. WBM without NPs
lost 8.3% of the PV value after the thermal exposition indicating that the gel structure was
devitalized. Hence, the degraded sample with SiC NPs presented PV conservation by 25%
higher than aged drilling fluid without NPs. However, drilling fluid with SiA NPs did not show
preservation after the aging process (See Figure 3-1.a).
Regarding YP values, the fresh samples increased by 15% with the SiC NPs and any
change for the SiA NPs. Aged drilling fluid without NPs reduced 16% of its YP value. The
aging process broke the gel structure for all samples. However, WBM with SiC NPs, the
Chapter 3 76
aging resulted in an increase in the YP by 19% regarding the aged WBM without NPs,
which confirmed the minor gel structure reduction. Contrary to the WBM with SiA NPs, YP
was reduced by 28% after the thermal exposition, even lower than the WBM without NPs
(See Figure 3-1.b). This behavior could affect the carrying capacity of the drilling fluid. An
increment in PV and YP due to SiC NPs addition allows the WBM to improve the clean well
and suspend the solid particles or consider a possible decrease in the viscosifying
additives, e.g., xanthan gum. Additionally, after the aging process, the preservation of PV
and YP indicates a minor loss of gel structure, less chain polymer breaking, increases the
valuable fluid life, and decreases the polymer amount during the drilling operation.
Figure 3-1: Plastic viscosity (VP) and b) yield point (YP) measured at 77°C of the BFWBM with and without the synthesized and fumed SiO2 NPs before and after the aging process at 77°C for 16 h.
Figure 3-2 shows the gel strength at 10 s, 10 m, and 30 m of WBM with 0.1 wt.% of SiA
and SiC NPs before and after the thermal degradation. Rheological measurements
revealed that the gel strength increased for the fresh drilling fluids by 25, 20, and 20%,
respectively, with the addition of 0.1 wt% SiA NPs; whereas SiC NPs increased by 50, 40,
and 40% for the exact times (see Figure 3-2.a). At ultra-low velocity, the WBM has its
highest yield stress values. Under static conditions, WBM develops a gel structure that aids
the solid particle suspension. This behavior is more remarkable for the SiC NPs. Also, the
gel strength of drilling fluids with SiO2 NPs showed the highest increase at the first 10
seconds; rapidly, the polymer built a structural network in static conditions. Aged drilling
fluid without NPs lost the 15, 20, and 20% of its 10s, 10min, and 30min gel strength
Chapter 3 77
measurements, respectively. Thermal degradation devitalized the mud gel structure in all
rheological parameters. However, the WBM with SiC NPs helped preserve this property
with an increment of 33, 25, 25% for the 10s, 10m, and 30m, respectively, compared with
the aged drilling fluid without NPs. Newly, the first 10 seconds presented the most
significant increase. SiA had a negative behavior reducing the gel strength; this could affect
the solid particle suspension and promote the precipitation (see Figure 3-2.b). The
evaluated time, 10s, 10m, and 30m, were improved notoriously for the addition of SiC NPs,
forming a more robust network between chain polymers. As discussed in Chapter 2, the
NPs favor the electrostatic forces present in the drilling fluid. At static conditions, the
attraction forces are strengthened, and at dynamic conditions, the electrostatic repulsion, a
task that is verified when the WBM has not been subjected to temperature exposure.
However, for the degraded fluid, the SiA NPs failed to preserve the polymer gel structure,
the breaking of the polymer chains is not inhibited. This parameter is essential when using
a drilling fluid in the field, where the drilling fluid undergoes degradation during the drilling
process.
Figure 3-2: Gel strength measured at 60°C of the WBM with and without the synthesized and fumed SiO2 NPs a) before (B.R) and b) after (A.R) aging process at 77°C for 16 h.
The effect of 0.1 wt.% SiA and SiC NPs on the viscosity as a function of the shear rate in
the WBM before (Figure 3-3.a) and after (Figure 3-3.b) thermal exposure is presented in
Figure 3-3. WBM samples exhibited shear thinning behavior, the viscosity decreases by
increasing the shear rate [27]. Xanthan gum chains are arranged as single helices
(repulsion) changing to coils (attraction) due to the shear rate, temperature, and ion strength
Chapter 3 78
[28]. For fresh drilling fluids in the presence of NPs (Figure 3-3.a), the viscosity increased
at low shear rate values (< 200 s-1) by 22.5 and 55.0% for the SiA and SiC NPs, respectively.
At high shear rates (> 200 s-1), the viscosity increased by 7.0 and 15.0% for the same order
of NPs compared with the WBM without NPs. After thermal exposure (Figure 3-3.b), WBM
in the absence of NPs reduced its viscosity by 22.5 and 11.0% at low and high shear rates,
respectively, compared with the fresh drilling fluid without NPs. Once again, WBM lost the
viscosity properties due to exposure to temperature conditions. However, the addition of
SiC NPs afforded an excellent resistance in this regard; the increase in viscosity at < 200
s-1 was 58.0%. At > 200 s-1, the drilling fluid presented better performance with an increment
of 21.0. The drilling fluid with SiA NPs did not present a significant inhibition of the thermal
degradation even presented viscosity values lower than the WBM without NPs. WBM
exposed at temperature would result in the degradation of the polymer. The temperature
and thermal degradation lead to loss of molecular weight and breakdown of polymer chains
reducing the steric stabilization [19]. The degradation caused the loss of properties and
effectiveness of polymers. Still, SiC NPs did not suffer the same degradation. WBM would
preserve these under degradative environments.
Figure 3-3: Viscosity of drilling fluids as a function of the shear rate in the absence and presence of 0.1 wt% SiA and SiC NPs at 77 ºC (a) before and (b) after the aging process.
The effect of the NPs at a fixed dosage of 0.1 wt.% at 60 ºC in the shear stress is shown
in Figure 3-4. As discussed above, it can be seen that the addition of SiO2 NPs increased
the shear stress at all shear rates when compared to the fresh base fluid without NPs
Chapter 3 79
(Figure 3-4.a). Nevertheless, SiC NPs caused the highest upward shift of the rheogram up
to +50.0% for shear rates between 500 and 1000 s-1 than the WBM, whereas SiA NPs
increased +20.0%. After thermal degradation (Figure 3-4.b), WBM without NPs showed a
shear stress reduction between 12.0 and 18.0% for low and high shear rates, respectively.
On the other hand, WBM containing SiC NPs exhibited good conservation of the properties
showed an increase. The opposite was observed for the SiA NPs; the shear stress of the
WBM was below WBM without NPs. SiA NPs promote polymer degradation. Whereas for
the SiC NPs, the adsorbed polymer must be situated onto the particle surface so that the
chains cannot desorb or move out due to an external process. Free or desorbed polymer
chains could suffer degradation [29].
Figure 3-4: Shear stress of drilling fluids as a function of the shear rate in the absence and presence of 0.1 wt% SiA and SiC NPs at 77 ºC. (a) before and (b) after the aging process.
The parameters of the Bingham Plastic (BP) and Herschel−Bulkley (HB) models are shown
in Table 3-1. The HB model had the best fit according to the values of the statistical
parameters, including the correlation coefficient (R2), with values > 0.99, and the root mean
square error (RMS), close to 1.0 %. The addition of 0.1 wt% SiC NPs improved the
rheological structure of the fresh drilling fluid, increasing 66.5 and 8.3% and reducing 8%
in the yield point (𝜏𝑜), consistency factor (𝐾), and the flow behavior index (𝑛); whereas SiA
NPs only represented a significative change in the 𝜏𝑜 with an increase of 56.3%. Although
factors 𝐾 and 𝑛 did not change substantially with the thermal rolling process in the drilling
fluid samples, the 𝜏𝑜 dramatically changed. Drilling fluid without NPs after thermal
Chapter 3 80
degradation reduced 46.0% the 𝜏𝑜, this indicates the lots of carrying capacity of solid
particles. However, adding 0.1 wt% SiC NPs into the drilling fluid allowed it to be 68.4%.
The addition of NPs conserves the rheological parameters after the aging process.
Higher 𝜏𝑜 and 𝐾 leads to drilling fluid higher viscosity and carrying capacity; this results in
better bottom hole cleaning and more efficiency during drilling. Moreover, lower 𝑛 generate
higher shear-thinning behavior (lower viscosity at higher shear rates and higher viscosity at
lower shear rates), which improves the hydraulic efficiency of the fluid. The SiC NPs could
be dispersed (repulsive forces), and the viscosity was reduced. In contrast, at low shear
rates, the SiC NPs could be agglomerated (attractive forces), and the fluid viscosity would
be increased [19].
Table 3-1: The yield point, plastic viscosity, flow consistency index, flow behavior index,
mean squared error, and the root mean square error treated as Bingham-plastic and
Herschel–Bulkley models the WBM contain 0.1 wt% SiA and SiC NPs at 60 ºC.
After the thermal rolling
process
Before the thermal rolling
process
SiO2 NPs concentration (wt.%)
Model 0.0 0.1SiA 0.1SiC 0.0 0.1SiA 0.1SiC
BP
𝝉𝒐 (𝒍𝒃 𝟏𝟎𝟎 𝒇𝒕𝟐⁄ ) 3.63 4.62 6.14 8.63 4.62 4.69
𝝁𝒑 (𝒄𝑷) 0.12 0.12 0.13 0.37 0.12 0.12
𝑹𝟐 0.9720 0.9770 0.9715 0.9740 0.9770 0.9744
𝑹𝑴𝑺 0.1330 0.1221 0.1412 0.2100 0.1221 0.1364
HB
𝝉𝒐 (𝒍𝒃𝒇. 𝟏𝟎𝟎 𝒇𝒕−𝟐) 1.76 2.75 2.93 0.95 1.30 2.55
𝑲 (𝒍𝒃𝒇. 𝟏𝟎𝟎 𝒇𝒕−𝟐𝒔𝒏) 0.65 0.63 1.05 0.61 0.52 0.62
𝒏 0.72 0.73 0.66 0.71 0.71 0.71
𝑹𝟐 0.9992 0.9996 0.9998 0.9997 0.9997 0.9997
𝑹𝑴𝑺 0.0284 0.0235 0.0097 0.1282 0.0123 0.0276
SiO2 NPs into the WBM significantly impacted the rheology, even higher after the
temperature exposure. The rheology alteration was notorious in the results with the
increase of the YP, PV, Gel strength, 𝐾, and the reduction of 𝑛. Also, SiO2 NPs, especially
Chapter 3 81
SiC NPs, reduce degradation and increase the WBM thermal resistance. Some authors
suggested that NPs interact with the solid particle as the bentonite and impact the bentonite
net surface charge. This charge alteration promotes the association through edge-to-face
(E-F) and edge-to-edge (E-F); these types of association enable the gel-like structure and
form a 3-D structure called a house of cards, increasing the viscosity and yield stress of the
fluids [30, 31]. However, in a WBM, the addition of CaCO3, a weighting and bridging
material, did not alter the WBM rheological properties [32, 33]. SiO2 NPs act as a dispersing
agent, allowing a good dispersion, where repulsion forces between NPs and CaCO3 play a
significant role due to the electronegativity of both. In this way, the aggregation was
avoided, obtaining a good dispersion of the particles. This concept only represented the
fluid integrity and not the rheology increment [32, 33]. SiO2 NPs could interact with the
polymer and increase SiO2 NPs–polymer attraction, causing an enhanced viscosity and gel
structure strengthening.
The rheological behavior of the drilling fluid improves in the presence of SiC NPs for both
fresh mud and post-aging mud, while SiA NPs only show good performance in the fresh
drilling fluid. This performance following that SiC>SiA in terms of d50, SBET, and more groups
-OH according to the intensity of the FTIR and the results discussed by Montes et al. [34],
(more details about NPs characterization can be found in chapter 1). The polymer
adsorption onto NPs through hydrogen bonding between the oxygen from xanthan gum
and the hydrogen of the SiO2 NPs surface (SiO-H···O-COH) or between the hydrogen
bonding from the xanthan gum and the oxygen of the SiO2 NPs surface (Si-O···H-COO). A
more significant amount of OH groups on the surface could allow the building of a
microstructure due to the stronger attractive forces, which increased the resistance of
polymers to move when shear stress is applied and improved the wellbore cleaning
efficiency [5]. This interaction positively influences the NPs stability by the effect of the steric
repulsion [35]. The helix conformation of the xanthan gum is stabilized by H bonds
(hydrogen bonding with NPs) and destabilized by electrostatic repulsion between
carboxylate groups along the chains (free or not adsorbed xanthan gum). Thus, at low SiO2
NPs interaction (SiA NPs), polymer chains assume coil conformation. On the other hand,
under high interaction (SiC NPs), xanthan chains are arranged in a helical conformation.
Thermal degradation occurs when the polymer changes its properties under the influence
of temperature. Initially, it causes the reduction of molecular weight and viscosity reduction.
Generally, the polymer suffers thermal degradation due to the disruption of the polymer
Chapter 3 82
backbone. Thermal energy removes a hydrogen atom from the polymer chain; this unstable
radical can react with other species or dissociate the polymer structure [36]. Also, the
polymer could suffer oxidation or hydrolytic decomposition in the ether linkage [37]. The
polymer adsorption onto NPs surfaces had been reported to increase the polymer thermal
stability with little impact on the polymer rheological properties [26]. Generally, NPs may
work as points between the polymer chains, which support the strengthening of the
viscoelastic structure of the WBM [38, 39]. According to the results, SiC NPs perform better
than SiA NPs in the thermal degradation inhibition. Besides the d50, SBET, adsorption
capacity (discus below) of SiC NPs higher than SiA NPs could explain the SiO2 NPs-
polymer interaction. However, it is not enough for determining the tested NPs surface
activity. In this sense, acid surface analysis had an essential role in thermal degradation.
The surface acidity follows the order SiA > SiC. As mentioned in Chapter 1, the acid sites
(Lewis and Brønsted acid sites) are related to the surface acidity, the total acidity increase,
and Bronsted and Lewis also increase [40]. The Brønsted acidity of silica silanol groups is
induced by the adsorption of acids (HCl) to such an extent that it leads to proton transfer
[41]. The H+ could interact with the ether linkage between them glucopyranose and break
the polymer chain. This type of interaction can be called acid hydrolysis. The acid treatment
provides very hydroxyl-rich silica surfaces, interacting with negative chemical groups (see
Figure 3-5).
Figure 3-5: Mechanism of interaction between SiA NPs and xanthan gum molecules. Polymer chain-breaking after thermal degradation.
Chapter 3 83
• Filtration properties
Table 3-2 shows the filtration volume, filter cake thickness, and permeability obtained in the
HPHT filtration test for the WBM in the presence and absence of 0.1 wt.% SiA and SiC
NPs. The SiA and SiC NPs exhibited the exact behavior of reducing the filtration volume,
filter cake thickness, and permeability up to +11, 66, and 71% compared with the fresh
WBM in the absence of NPs. After thermal degradation, the higher reduction of filtration
volume, filter cake thickness, and permeability were obtained for the Si11C NPs with 17.6,
31.7, and 31.9%, respectively, due to the inhibition of the viscosity degradation of the
polymer after the temperature exposure.
Table 3-2: Filtration volume, mudcake thickness, and mudcake permeability calculated from Darcy's Law of the mudcake and respective reduction of the filtration test obtained under HPHT conditions WBM in the presence and absence of 0.1 wt.% SiA and SiC NPs.
Before the thermal rolling
process After the thermal rolling process
SiO2 NPs concentration (wt.%)
0.0 0.1 SiA 0.1 SiC 0.0 0.1 SiA 0.1 SiC
𝑽𝒇 (mL) 18 16 15.6 17 15 14
𝒉𝒎𝒄 (mm) 0,200 0,067 0,061 0,303 0,220 0,207
𝑲𝒎𝒄 (µD) 0,1861 0,0551 0,0534 0,2666 0,1706 0,1816
PPT tests were carried out to measure the plugging capability of the SiO2 NPs before and
after the thermal degradation. The spurt loss, filtration volume at 30 min, and total filtration
volume are shown in Table 3-3. The WBM without NPs did not have an optimized bridging
or filtration volume control; a large volume was obtained, making the effect of SiO2 NPs
more evident. The addition of 0.1 wt.% SiA and SiC NPs reduced the spurt loss and total
filtration volume by 14 and 50%, respectively, compared with the fresh WBM without NPs.
Both NPs had similar behavior because the viscosity does not increase too much when the
fluid is new.
After the thermal degradation, the WBM without NPs increased the spurt loss and filtration
volume, indicating that WBM did not plug the ceramic disks pores (diameter 20 µm). At high
temperatures and mechanical degradation, polymers are not thermally stable, which might
be the reason for high spurt loss and filtration volume values. The fluid lost the colloidal
stability, and the solid particles were precipitated [32]. However, this situation was avoided
Chapter 3 84
by the SiC NPs addition. Spurt loss and total filtration volume were reduced by 66 and 49%,
respectively. Spurt loss less than 2mL is expected [41]; as shown in Table 3-3, the SiC NPs
were the only ones accomplished. Particularly in the PPT test, the pressure exerted on the
fluid is contrary to the HPHT test. That is, gravitational phenomena are more noticeable. In
this way, the correct suspension of the particles in the fluid plays a significant role. The
breaking of the polymer chains reduces the colloidal stability of the suspension, the particles
aggregate, and due to gravitational effects are deposited, the bridging capacity of the fluid
is reduced, allowing high filtration rates. The filtration volume differences volume between
the SiA and SiC NPs after thermal degradation were related to their different pore plugging
ability due to the xanthan gum affinity, where SiC NPs presented the highest affinity. The
physicochemical mechanism occurs when the NPs promote the repulsion forces caused by
the negative charge surface [30]. Hydrophilic NPs showed a high performance in WBM;
NPs were stable in aqueous solution and did not aggregate themselves, even acted as
dispersing agents.
Table 3-3: Spurt loss, filtration volume at 30 min, and total filtration volume of the filtration test obtained under HPHT conditions of the WBM in the presence and absence of 0.1 wt.% SiA and SiC NPs.
Before the thermal rolling process After the thermal rolling process
SiO2 NPs concentration (wt. %)
0.0 0.1 SiA 0.1 SiC 0.0 0.1 SiA 0.1 SiC
Spurt loss (mL) 3.5 3 3 7.5 5.5 2.5
Filtration
volume – 30
min (mL)
12.5 5.5 6 14.5 13 8
Total filtration
volume (mL) 28.5 14 15 36.5 31.5 18.5
• Adsorption isotherms
Effective steric stabilization is when several conditions are considered. High surface area
and affinity between molecules to ensure high solid particle coverage. Suitable solvent to
improve the repulsive forces between the solid particle coverage by the polymer. Low free
polymer concentration to avoid the depletion attractions [1]. Figure 3-6 showed the
Chapter 3 85
adsorption isotherms when the SiA, SiC NPs, and CaCO3 concentrations were fixed in
solutions varying the xanthan gum concentration. Isotherms obtained for NPs
corresponded to Type I, according to IUPAC [42]. Hence, the polymer concentration
polymer rises, aggregate size increase [38]. The attractive forces became stronger. Auto-
associative activity is due to the polymer functional groups reducing the SiO2 Nps-polymer
interactions and adsorbed capacity. The systems adsorbed rapidly reached the available
surface area saturation, so the graph resulted in a plateau for high polymer concentrations.
For CaCO3, according to the IUPAC classification, it corresponds to type III [42]. Xanthan
gum has approximately the same affinity for CaCO3 or is slightly more affinity to xanthan
gum molecules. CaCO3 is a micrometric material; its surface area is smaller; therefore, few
functional groups are exposed on the surface to interact with xanthan gum. Once the
polymer accomplishes to adsorb onto CaCO3, given their self-associative nature, they form
several layers of polymer on the CaCO3 surface, physisorption, or multilayer adsorption;
the polymer also acts as a free site for another polymer molecule to adsorb. This adsorption
mechanism is characterized by low absorption energy and low stability that can be easily
removed [26, 43]. Strong repulsions are obtained with high polymer surface coverage. At
low adsorption, bridging interactions might otherwise result. The adsorbing polymer needs
to show a plateau region in the adsorption isotherm [1]. Based on molecular dynamic
simulation results, the xanthan gum interacts the most with NPs, followed by the CaCO3.
Additionally, the xanthan gum molecules approach each other closer when a solid surface
such as CaCO3 is presented [33].
The SLE model described the experimental results with RMS% < 10% values% in the right
way%, see Table 3-4. The 𝐻 parameter defines the affinity between adsorbate and
absorbent and is related to the curve slope monolayer adsorptions. The 𝐾 parameter is
associated with the adsorbate-absorbent aggregation degree, how many molecules are
located in the multilayer. The system with the lowest 𝐻 and 𝐾 parameters has the highest
affinity and lowest self-aggregation. Therefore, it can be observed that the 𝐻 and 𝐾
parameters for the SiC NPs corresponded to the lowest values, compared with the SiA NPs
and CaCO3. SiC NPs surface had a great affinity with the polymer molecules and a low
polymer self-association in the surrounding surface. The SiC Nps-xanthan gum interactions
are more potent than between the SiA NPs and CaCO3 with the polymer. Additionally, the
Chapter 3 86
𝑁𝑎𝑑𝑠,𝑚 Corresponding to SiC NPs is greater than SiA NPs due to the higher surface area
presented by NPs (see section 1.2.1.). The greater the surface area, the greater the active
sites or functional groups interact with the polymer [44]. The adsorption in the SiO2 NPs-
polymer occurs mainly due to silanol functional groups, the -OH groups, the free radicals in
the xanthan gum, and the carboxylic groups -COOH [45]. According to the FTIR spectrum
of the SiC NPs, this material presented a more significant presence of -OH groups on the
surface; this could explain why affinity is more pronounced for the SiC NPs-polymer
interaction. Although the amount adsorbed for CaCO3 is higher according to the SLE model,
this amount corresponds to layers of polymer molecules that can be easily removed.
Figure 3-6: Adsorption isotherms of xanthan gum onto SiA, SiC NPs, and CaCO3 particles (1000 mg. L-1) obtained varying the initial polymer concentration (100-2500 mg. L-1) and a fixed temperature of 25°C.
Table 3-4: Estimated SLE model parameters for polymer adsorption onto SiA, SiC NPs, and CaCO3 particles (1000 mg. L-1) obtained varying the initial polymer concentration (100-2000 mg. L-1) and a fixed temperature of 25°C.
Adsorbent (wt.%)
𝑯 (𝒎𝒈. 𝒈−𝟏) 𝑲 𝒙 𝟏𝟎−𝟑(𝒈. 𝒈−𝟏) 𝑵𝒂𝒅𝒔,𝒎(𝒎𝒈. 𝒈−𝟏) RMS%
0.1 SiA 5.13 9.8 189.24 10.16
0.1 SiC 2.91 6.8 195.32 9.23
Chapter 3 87
0.1 CaCO3 130.30 29.24 803.87 4.88
• The aggregate size of the SiO2 NPs-polymer system.
Figure 3-7 PSD of xanthan gum at 500 mg. L-1 in the presence of SiO2 NPs fresh and
degraded. DLS technique presented the hydrodynamic diameter of the aggregates. Thus,
according to the results, several polymer aggregates were found in helix and coil
conformation. Silanol groups on the surface of the SiO2 NPs can interact through hydrogen
bonding with the carboxylic groups (COOH) on the xanthan gum polymer chains [45]. At
high pH, the silanol groups become ionized. In this way, the repulsion forces to be strong
compared with the attraction forces between themselves. Thus, NPs avoid polymer
aggregation, which did not coil, mean aggregate size of the polymer is reduced in the
presence of NPs. After the aging process, the polymer aggregate size without NPs was
drastically reduced by 51%. Polymer degradation broke the chain polymer and lost the
ability to aggregate itself [46]. Results indicate that the polymer solution in SiC NPs
conserved the aggregate size reduced only 22% from the polymer solution without NPs.
Polymer breaking was inhibited, and this was corroborated with the preservation of the
viscosity properties discussed above. In contrast, SiA NPs reduced the aggregate size by
32%, and the viscosity was reduced. Long and flexible chains allow increasing the space
between NPs and solid particles, favoring greater electrostatic repulsion. The aggregate
size was measured only in the presence of NPs; the thermal degradation affects the
colloidal stability, especially the steric repulsion, which promotes the particles aggregation
and posterior settling (CaCO3). Whereas only with the NPs, the author did not find deposited
particles but if viscosity reduction.
Chapter 3 88
Figure 3-7: PSD of xanthan gum at 500 mg. L-1 in the presence of SiO2 NPs fresh and degraded.
Table 3-5: Mean aggregate size of xanthan gum at 500 mg. L-1 in the presence of SiO2 NPs fresh and degraded.
Xanthan gum – SiO2 NPs
(0.1 wt.%)
Mean aggregate size (nm)
Fresh Degraded
- 42289 21297
SiA 42289 28638
SiC 40436 31484
3.2. Partial conclusions
The addition of SiC NPs inhibited thermal degradation. The SiO2 NPs-xanthan gum
interaction through the adsorption process leads to the chain polymer hindering some
polymer functional groups that would be disabled to react with the oxygen in dry air. The
SiC NPs presented the highest adsorption capacity due to the quantity of -OH groups on
the NPs surface.
PPT filtration test was carried out for SiA and SiC NPs. The SiC NPs had the highest
filtration volume and filter cake thickness reduction after the aging process acting as loss
material additive to reduce the filtration volume due to their nanometric size and inhibiting
the polymer degradation. With SiC NPs, spurt loss and total filtration volume were reduced
Chapter 3 89
by 66 and 49%, respectively. SiA NPs did not have substantial effects on the reduction after
degradation.
The SiC NPs evaluated in this study improve the efficiency of the drilling fluid in terms of
thermal degradation, reducing the filtration volume, the filter cake thickness, and
permeability represent a viable alternative to expanding the range of conditions for the use
of NPs in the field application.
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Chapter 3 93
4. Effect of SiO2 NPs on external filter cake morphology of colloidal suspensions
The solid phase particles of the WBM, CaCO3, block the pores, forming the wellbore wall
filter cake [1-3]. The filter cake is divided into two sections. In the internal filter cake, smaller
particles invaded into porous media and blocked the pore throats near-wellbore. The larger
size is retained on the porous rock surface, and smaller particles and polymers build-up the
external filter cake [4]. Thin, flexible, and low permeable filter cake formed on the wall is
desired to reduce and prevent the formation damage of solid and mud filtrate invasion,
water phase trap, avoid pipe sticking, improve the well logging answer, and the wellbore
strengthening [5-7].
The deposition of particles is controlled by hydrodynamic forces, while surface forces
control the detachment. Once the particles are deposited, drag, permeate, lift, buoyancy,
and electrostatic forces act. Electrostatic and permeate flux forces adhere the particle to
the surface and depend on the size, shape, and zeta potential of the particle and fluid
properties such as pH and ion strength. The drag, lift, and gravitational forces constantly
erode the filter cake surface, producing surface roughness [4, 8, 9]. The colloidal
suspension stability has a significant effect on filtration. The filtrate of the flocculated
suspension (lower colloidal stability – particles aggregation) is higher than dispersed drilling
fluids. Thicker filter cakes are obtained in lower colloidal suspension stability, higher
permeability [8].
According to WBM design, filtration control additives (i.e., starch, polyanionic cellulose, etc.)
and sized CaCO3 help reduce the mud filtrate invasion formation [10]. Theoretically, the
larger particles are deposit first in the external filter cake, and then smaller particles are
deposited over the surface [8, 11, 12]. However, the CaCO3 micrometric particle size could
not seal the pores, aggregate, and lost colloidal stability [4]. With the recent development
Chapter 4 96
in nanotechnology, NPs improve the drilling fluid properties [13-15]. Filtration [16-20] and
rheological [21-23] properties have been most studied. NPs could reduce the solid particle
and mud filtrate invasion and inhibit the formation damage. NPs can form a better filter cake
in the first minutes of the drilling operation and develop a thinner and low-permeable filter
cake [24, 25]. Barry et al. [26] found that the filter cake permeability, filtration volume, and
structure are influenced by the intercalated clay NPs (ICH) and the clays under HTHP
conditions. ICH added exhibit rigid networks and low permeability filter cakes due to the
strong network with the clays. Mahmoud et al. [27] evaluated the influence of ferric oxide
(Fe2O3) NPs on the filter cake characteristics. The authors found that the filter cake density
increases as the NPs concentration increase. NPs changed the filter cake structure,
reducing the spaces and generating a smoother surface. Despite the studies presented
above by scanning electron microscopy (SEM) image [7, 20, 27, 28], and computed
tomography (CT) [27], most of the studies are analyzed descriptively. They do not define
the interaction mechanism of SiO2 NPs-drilling fluid components and changes in the internal
structure of the filter cake. No research involves a very high-resolution type of scanning
microscopy to evaluate the topography.
The porous structure, particles, pore size distribution, and texture of filter cake are some of
the most critical factors that define the degree of particle packing. Instead, we focused this
chapter on studying the effect of SiO2 NPs in the filtration and the build-up mechanisms of
the external filter cake of WBM through SEM and atomic force microscopy (AFM) image
processing. Particle and pore size distribution, porosity, and physical properties of the
external filter cake were studied to determine the electrochemical interactions of the SiO2
NPs-WBM components. The image processing presented in this work contributes to a
better phenomenological understanding of the filter cake build-up mechanism in the
presence of SiO2 NPs. In this sense, we obtained insights that clarified the synergy of the
SiO2 NPs-CaCO3, the morphological structure, surface roughness, and its impact on the
filtration volume.
4.1. Experimental
4.1.1. Material
The filter cakes used were obtained from the PPT filtration test, according to the procedure
explained in section 3.1.2. According to the colloidal suspension thermal stability results in
Chapter 4 97
the presence of NPs and the processes of NPs fabrication thinking in a field application,
the filter cake obtained for the SiC NPs was evaluated, see chapter 3. SiC NPs will be called
SiO2 NPs from now on until the end of the thesis.
4.1.2. Methods
• SEM analysis
The filter cake morphology was characterized using an SEM (JSM7401, JEOL, Japan).
Filter cakes were dry at the temperature room for 24 hours. Tiny pieces (about 15 mm x 15
mm) were cut and coated with gold to analyze the filter cake surface. For the cross-
sectional, little pieces of cake were cut and coated the faces with gold. The SEM
observation was carried at magnification 300X and 200X for the top and cross-sectional
views, respectively. Additionally, the face corresponding to the cross-sectional view was
divided into four different layers, and different photograms were taken at various points.
Photograms correspond to at least four or three images to ensure reproducibility. Finally,
image analysis using free software Image J employed 200 particles for each photogram
[29]. Also, the pore size distribution of filter mudcake was determined using the method
developed by Rabbani et al. (2017). The methodology considered the darker spaces of the
filter cake surface as pores where the mud filtrate flows. Using multi-level thresholding over
gray-scale SEM image [30], detecting the image darkest portion [31]. Finally, energy
dispersive spectroscopy (EDS) was used to analyze the bottom and surface filter cakes.
Figure 4-1 summarizes the methodology employed to morphologically characterized the
filter cakes.
• AFM analysis
Roughness surfaces of the filter cakes in the absence and presence of NPs were evaluated
using AFM 5500 (Agilent Technologies, Chandler, AZ) equipment. The AFM images were
taken in tapping mode; the acquisition speed was 0.2-0.3 lines per second, the resolution
of the pictures was 512 points per line, the cantilever resonance frequency was 236 kHz,
length 5 µm, and width 5 µm. The AFM images were analyzed using Gwyddion software
[32]. The surface roughness of the samples was analyzed through several parameters:
mean roughness (Ra), mean square roughness (RMS), surface skewness (Rsk), and
kurtosis coefficient (Rku). The parameters were calculated for each row according to the
Chapter 4 98
Gywddion tool [33]. Figure 4-1 summarizes the methodology employed to morphologically
characterized the filter cakes.
Figure 4-1: Overview of the experimental analyses used in this study.
4.2. Results
4.2.1. SEM Analysis
Figure 4-2 shows the SEM photographs of the top view of the filter cakes from WBM in the
absence and presence of SiO2 NPs. Random deposition of angular solid particles formed
the external filter cake with many spaces between the CaCO3, which are favorable for the
invasion of the mud filtrate for the filter cake in the absence of NPs. NPs formed a denser
filter cake surface, fewer pores, and thinner solid particles to obtain a more homogenous
surface. The addition of NPs changed the external filter cake morphology, which appears
to be less porous and permeable than the filter cake without NPs, as shown in Figure 4-3.b.
According to the cross-section view, the larger particles are deposited in the bottom, smaller
particles as the external filter cake thickness grow, as shown in Figure 4-3. The transition
from larger to smaller particles is faster for the filter cake with SiO2 NPs (red line), and the
filter cake presented a tighter structure. As particles are deposited, the filter cake thickness
increase. If the porosity decrease, the permeate flux is decreasing allowing the transition
from larger to smaller particles quickly. SiO2 NPs reduce the filter cake porosity since the
Chapter 4 99
first solid particles are deposited. Then, smaller and smaller particles settle on the filter cake
surface. Thus, it allowed the reduction of the filter cake thickness with SiO2 NPs by 8%.
The thickness reduction and improvement of the filter cake morphology in the presence of
NPs suggest two mechanisms of action. A stable colloidal suspension, solid particles
dispersed in the fluid, allows an orderly deposition of particles on the porous medium. If the
drilling fluid is flocculated or the CaCO3 is aggregate, an aggregates deposition and spaces
will enable the mud filtrate invasion. The NPs favor the electrostatic repulsive forces in the
colloidal suspension due to their surface charge and the distance between particles
(Chapter 2). Additionally, the polymer adsorbed onto the particles, increasing steric
repulsion forces (Chapter 3). Once CaCO3 is deposited due to the filtration process, the
NPs reduce the filter cake porosity by occupying the spaces between CaCO3. The distance
between the particles decreases, increasing the attractive forces. Through molecular
simulation, these results were corroborated. The non-bonded interaction energy between
the CaCO3 was 21 kcal∙mol-1, whereas, in the presence of the NPs, it is only 1.87x10-5 kcal
∙ mol-1. Accordingly, the presence of the NPs almost diminishes the repulsive interaction
energy between the CaCO3 [38]. Finally, the polymer also coverage the particles and
reduce porosity (chapter 2).
The presence of NPs promotes these repulsive forces due to the electrical double layer
increasing or promoting the negative ions concentration onto the CaCO3 surface while
particles are separated. After the filtration process, the distance between particles is
drastically reduced. When two charged particles, NPs and CaCO3, come close to each
other, their diffuse layers overlap and start to interact. The electrostatic double-layer charge
is reversed with a small surface separation distance, and the interaction energy may be
attractive with surface potentials of the equal sign [39]. In this case, the surface with the
lower magnitude potential, CaCO3 (-28.60 mV CaCO3), is forced to charge changes sign to
positive. It means that there must be an attractive component of force between the NPs
and CaCO3. However, this attraction must arise from an electrical double-layer interaction
and not attractive Van der Walls forces [39]. The electrostatic double-layer interaction is
mainly dependent on the surface potential. NPs alter the CaCO3 surface potential and
influence ion distribution across the diffuse layer and into the bulk solution.
Chapter 4 100
Figure 4-2: SEM photographs (X300-50 µm magnification) of the top surface view of the filter cake generated by the a) WBM and b) WBM with 0.1 wt.% SiO2 NPs.
a)
b)
Chapter 4 101
Figure 4-3: SEM photographs (X55-200 µm magnification) of the cross-section view of the filter cake generated by the a) WBM and b) WBM with 0.1 wt.% SiO2 NPs.
According to the methodology, the filter cake cross-section was divided into four layers.
Figure 4-4 to Figure 4-7 presents the SEM photograms, their corresponding processed
images, and the particle and pore size distribution for each layer in the absence and
presence of SiO2 NPs. Table 4-1 summarize filter cake layer properties from image
processing analysis. Figure 4-4 shows layer one. Large particles and larger pore throat
sizes predominate; during the first minutes of filtration, the large particles of the WBM
formulation (mesh 200= 20 – 30 µm) were deposited while fines particles pass through
invaded the formation, thus the low presence of fine particles. The porosity of this layer is
the highest among the other layer. However, the filter cake with SiO2 NPs showed a slight
reduction. During the formation of layer one, the most significant volume of mud filtrate are
present. However, SiO2 NPs control mud filtrate invasion, as was observed in the spurt loss
reductions (chapter 3). The low standard deviation indicates that most particle size tends
to close to their mean value and not random deposition of particles.
The morphology for layer two is shown in Figure 4-5. This layer presented a higher degree
of compaction compared to layer one. SiO2 NPs reduced the mean particle-sized deposited,
the standard deviation, mean pore throat size, and porosity compared to filter cake without
NPs. Whereas the filter cake without NPs showed similar characteristics to layer one. No
definite transition from larger to smaller particles is observed. In contrast, the filter cake
layer two with SiO2 NPs presented other deposition patterns.
a
)
b
)
Chapter 4 102
Figure 4-6 and Figure 4-7 presented the layer three and four, respectively. For filter cake
with SiO2 NPs, the lower mean particle and pore throat size and porosity were reached
since layer three. Layer four showed similar values. Whereas layers three and four without
NPs, these parameters are still more significant than those observed for filter cake with NP
(see Figure 4-7.b). WBM without NPs needed an additional layer or more time to reach and
low-permeable and porosity filter cake. Layer four with SiO2 NPs predominates fines
particles (mesh 600 and 1200= 7 y 10 µm). The filter cake layer without NPs still presented
a larger particle size (between 20 – 30 µm). The transition from large to smaller particles
means pore throat size and porosity reduction.
The recompilation of the pore size distribution for each filter cake layer is shown in Figure
4-8. The presence of NPs allowed a faster transition since layer two, layer three, and layer
four presented similar distribution. Filter cake without NPs showed a gradual change, and
the filter cake layer four must reach lower porosity. NPs allowed the particle packing,
greater attraction forces, and plugged pores effectively with fines particles.
As discussed above, large particles deposition at the filter cake base and subsequent fine
particles deposition to the top [8]. The reduction of the permeate flux indicates the
deposition of fine particles. Thus, the faster the filtration flux decreases, the quicker the
presence of fine particles, and this behavior was observed for filter cake with NPs. A thinner
and more compact filter cake was obtained. It results in less fluid filtration. It is necessary
to form a low-permeable filter cake at the early time of drilling operation since it reduces
fluid loss and creates the thin filter cake. According to the studies developed by Jiao et al.
[8], this model of cake growth is with the mean particle size in the cake decreasing as the
cake builds up, according to the experimental evaluation of each filter cake layer.
Chapter 4 103
Figure 4-4: SEM photographs (X200-100 µm magnification) and processed images of two different zones of the filter cake layer one and the average particle and pore size distribution (histogram and normal fitting) generated by the filter cake from the a) WBM and b) WBM with 0.1 wt.% SiO2 NPs.
SEM photogram Binary segmentation Particle and pore size
distribution
a)
b)
Chapter 4 104
Figure 4-5: SEM photographs (X200-100 µm magnification) and processed images of two different zones of the filter cake layer two and the average particle and pore size distribution (histogram and normal fitting) generated by the filter cake from the a) WBM and b) WBM with 0.1 wt.% SiO2 NPs.
SEM photogram Binary segmentation Particle and pore size
distribution
a)
b)
Chapter 4 105
Figure 4-6: SEM photographs (X200-100 µm magnification) and processed images of two different zones of the filter cake layer three and the average particle and pore size distribution (histogram and normal fitting) generated by the filter cake from the a) WBM and b) WBM with 0.1 wt.% SiO2 NPs.
SEM photogram Binary segmentation Particle and pore size
distribution
a)
b)
Chapter 4 106
Figure 4-7: SEM photographs (X200-100 µm magnification) and processed images of two different zones of the filter cake layer four and the average particle and pore size distribution (histogram and normal fitting) generated by the filter cake from the a) WBM and b) WBM with 0.1 wt.% SiO2 NPs.
SEM photogram Binary segmentation Particle and pore size
distribution
a)
b)
Chapter 4 107
Figure 4-8: The particle size distribution of filter cake layers one to four generated from the a) WBM and b) WBM with 0.1 wt.% SiO2 NPs.
Table 4-1: Filter cake layer properties from image processing analysis
SiO2 NPs
concentration
(wt.%)
Layer
Mean
particle
size (µm)
Mean pore
size (µm)
Porosity
(%)
Standard
deviation
WBM
1 39.21 3.34 16.10 2.82
2 27.39 2.19 12.56 1.31
3 15.69 1.95 12.81 1.06
4 11.09 2.11 12.90 1. 14
0.1
1 35.33 2.17 15.66 1.40
2 20.19 1.96 8.48 1.17
3 9.68 1.98 11.88 1.14
4 9.41 1.94 12.10 1.10
Figure 4-9 shows the EDS spectrum analysis of the bottom (layer one) and top (layer four)
of the filter cake in the absence and presence of SiO2 NPs. The calcium (Ca) appeared
because the CaCO3 was used as a bridging material; the carbon (C) was referred to as
organic compounds, polymers, and CaCO3. For the filter cake with NPs, both layers of the
filter cake counted silicon (Si), being the bottom side presented the highest Si concentration
by 1.48% compared with the top surface, 0.42%; less than 70%. SiO2 NPs could enter and
a) b)
Chapter 4 108
occupied the spaces between CaO3, reducing the porosity of layer one that presented the
higher permeability and porosity.
Figure 4-9: EDS analysis of the filter cake samples generated by the drilling fluids in the presence and absence of SiO2 NPs for (a) bottom surface and (b) top surface
Within the WBM, CaCO3 particles contributed to the filter cake build-up forming a physical
barrier to prevent fluid loss [13]. Moreover, xanthan gum interaction with CaCO3
strengthened the filter cake as the polymer fills the void among CaCO3 particles [34].
Xanthan gum attachment to the CaCO3 particles arises from the electrostatic interactions
between the anionic polymer groups and the hydrated calcium sites on the CaCO3 surface.
The predominant surface ions on CaCO3 are Ca2+ and CO32-, at pH values between 7 and
12 [35]; calcium ions screen the negative surface charges of the –OH groups of the polymer
and reduce the electrostatic repulsive forces [35-37]. Upon adsorption onto the CaCO3
particles, the NPs reduced the electrostatic repulsion among the deposited CaCO3
particles, favoring particle attraction and a more compact filter cake [14]. The zeta potential
of the CaCO3 at pH= 10 was -28.60 mV [38], which falls at the limit of the unstable region.
The NPs interact through their silanol (Si-OH) and hydroxyl (‒OH) groups with the C‒O
groups of the CaCO3 via hydrogen bonding, thus reduces the impact of the repulsive
electrostatic forces due to CO32-. On the other hand, xanthan gum is more likely to react
with the positive charges of surface Ca2+ [35]. NPs leads to a much firmer and more
compact filter cake, which is again in line with the experimental results. The NPs
Chapter 4 109
preferentially adsorb onto the Ca2+ surface sites and bridge between the slabs with Van der
Waals interactions, reducing the overall repulsive interaction among the calcite slabs (see
Figure 4-10).
Figure 4-10: Mechanism of interactions once the solid particle is deposited in the filter cake surface.
4.2.2. AFM analysis
2D and 3D AFM images were used to analyze the surface morphology of the bottom and
top surface of the filter cake in the absence and presence of SiO2 NPs, as shown in Figure
4-11 and Figure 4-12, respectively. The average surface roughness profile for the bottom
and top surface of the filter cake is shown in Figure 4-13. The statistics parameters are
given in Table 4-2. For the bottom filter cakes with SiO2 NPs, Figure 4-11.b shows tightly
packed particles and presents a smooth surface, like a particle coating, compared with the
filter cake in the absence of NPs. Regarding filter cake without NPs revealed a granular
morphology with larger particles and valleys between them. The statistical Ra parameter
corroborated that the filter cake with NPs is 31% less than the bottom without NPs. Also,
the RMS suggested that the deviation average is lower for the filter cake with SiO2 NPs.
The Rsk and Rku parameters indicated good symmetry of the profile variation with a value
near zero, although bad uniformity for the filter cake with SiO2 NPs with a lower value of
Rku.
Chapter 4 110
Regarding the top surface, in Figure 4-12, thinner particles are deposited in the surface,
and a smoother surface was obtained for the filter cake in the presence of SiO2 NPs, as
shown in Figure 4-12.b. Also, small valleys are situated between the packed particles
reducing the space where the mud filtrate can pass through. Whereas filter cake without
NPs presented large particles, valleys, peaks predominate, and an irregular surface. Ra
and RMS parameters of the filter cake with NPs showed lower values similar to the bottom
surface. The Rku parameter suggested a uniform surface with a value equal to three,
representing the kurtosis for a standard normal distribution. The results agree that cross-
sectional SEM photographs through different layers show large particle and pore size at
the first layer (bottom surface) and thinner and packed at the last one (top surface). NPs
can improve cake formation quality, making a smoother cake surface, less solid particle
erosion. Also, NPs contributed to a denser filter cake with high packing among the particles.
Hence fewer pores and cracks appeared due to the attraction forces between CaCO3 and
NPs.
Chapter 4 111
Figure 4-11: AFM 2D images (topography map) ad their respective 3D images (space distribution) of three different zones of the bottom view of the filter cake that have SiO2 NPs concentration of (a) 0.0 wt.%, and (b) 0.1 wt.%.
a)
b)
Chapter 4 112
Figure 4-12: AFM 2D images (topography map) ad their respective 3D images (space distribution) of three different zones of the top view of the filter cake that have SiO2 NPs concentration of (a) 0.0 wt.%, and (b) 0.1 wt.%.
a)
b)
Chapter 4 113
Figure 4-13: Average roughness profile for the filter cake generated by the drilling fluids in the absence and presence of SiO2 NPs at 0.1 wt% of (a) bottom, and (b) top view
Table 4-2: The properties of fresh fouled, physical cleaning, and chemical cleaning membranes
Properties
SiO2 NPs concentration (wt.%)
0.0 0.1 0.0 0.1
Bottom view Top view
Ra (µm) 0.0819 0.0560 0.0778 0.0513
RMS (µm) 0.1075 0.0710 0.1019 0.0730
Rsk (µm) -0.1736 0.0843 -0.2365 -0.3507
Rku (µm) 0.9240 0.2968 1.4077 3.5792
SiO2 NPs improve the filter cake properties by reducing the filtration volume and the
thickness working in synergy with the CaCO3 due to physical and electrochemical
mechanisms, as shown in Figure 4-14. During the first minutes of the drilling operation,
large particles are deposited due to the high permeate flux to the formation; as this flow
decrease with the particle deposition, smaller particles are deposited. SiO2 NPs occupy
Chapter 4 114
the empty spaces, placing between the bridging material. SiO2 NPs-CaCO3 interaction
increase through the attractive forces between them and achieving a more compact
filter cake, contributing to the permeability reduction. NPs could seal the pores due to
the high attraction force towards the surface. The high concentration of NPs at the filter
cake base and low concentration on the surface. Eventually, with the permeate flux
reduction, smaller and smaller particles will deposit on the cake surface. A smoother
surface and low-permeable filter cake are obtained. Thus, the transition from large to
smaller particles is obtained faster due to SiO2 NPs that improve the filter cake packing
reducing filtration (red dotted lines). This cake growth mechanism gives rise to a
heterogeneous cake with a predominant presence of large particles, a lower presence
of fine particles at the bottom, and small particles on the top surface.
Figure 4-14: Schematic illustration of the physical and electrochemical mechanism between SiO2 NPs-CaCO3 during filter cake formation.
4.3. Partial conclusions
• SiO2 NPs modify the morphological structure and thickness of the filter cake through
physical and electrochemical interactions. Large particles are deposited in the
bottom of the filter cake. As the filtrate flow decreases, smaller particles are
deposited on the top surface. SiO2 NPs allow a faster transition from larger to
smaller particles due to reducing the filter cake permeability and porosity.
Chapter 4 115
• SiO2 NPs occupy the space between CaCO3 and increase the attractive forces
obtaining a more compact filter cake with fewer pore spaces. SiO2 NPs plug the tiny
pores due to the high affinity with the porous media, so NPs are concentrated in the
filter cake bottom layer.
• The roughness surface of both the bottom and the top is reduced with the addition
of SiO2 NPs to the drilling fluid, obtaining a smoother, uniform, and a less porous
surface. Thus, it allows the presence of fewer flow canals with less pore throat size.
• The application of techniques SEM and AFM in drilling fluid engineering can be an
emergent analysis to evaluate the morphology and build-up mechanisms of the filter
cake
4.4. References
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[2] S. Elkatatny, M. Mahmoud, and H. A. Nasr-El-Din, "Filter cake properties of water-based drilling fluids under static and dynamic conditions using computed tomography scan," Journal of Energy Resources Technology, vol. 135, p. 042201, 2013.
[3] R. Yao, G. Jiang, W. Li, T. Deng, and H. Zhang, "Effect of water-based drilling fluid components on filter cake structure," Powder Technology, vol. 262, pp. 51-61, 2014.
[4] J. Dorman, I. Lakatos, G. Szentes, and A. Meidl, "Mitigation of formation damage and wellbore instability in unconventional reservoirs using improved particle size analysis and design of drilling fluids," in SPE European Formation Damage Conference and Exhibition, 2015.
[5] S. Elkatatny, M. A. Mahmoud, and H. A. Nasr-El-Din, "Characterization of filter cake generated by water-based drilling fluids using CT scan," SPE Drilling & Completion, vol. 27, pp. 282-293, 2012.
[6] X. Liu and F. Civan, "Formation damage and skin factor due to filter cake formation and fines migration in the near-wellbore region," in SPE formation damage control symposium, 1994.
[7] O. Mahmoud, H. A. Nasr-El-Din, Z. Vryzas, and V. Kelessidis, "Effect of ferric oxide nanoparticles on the properties of filter cake formed by calcium bentonite-based drilling muds," SPE Drilling & Completion, vol. 33, pp. 363-376, 2018.
[8] D. Jiao and M. M. Sharma, "Mechanism of cake buildup in crossflow filtration of colloidal suspensions," Journal of Colloid and Interface Science, vol. 162, pp. 454-462, 1994.
[9] A. Kalantariasl and P. Bedrikovetsky, "Stabilization of external filter cake by colloidal forces in a “well–reservoir” system," Industrial & Engineering Chemistry Research, vol. 53, pp. 930-944, 2014.
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Chapter 4 116
[11] F. Civan, "Chapter 18-Drilling mud filtrate and solids invasion and mudcake formation, Reservoir Formation Damage," ed: Burlington: Gulf Professional Publishing, 2007.
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[13] L. Whatley, R. Barati, Z. Kessler, and J.-S. Tsau, "Water-Based Drill-In Fluid Optimization Using Polyelectrolyte Complex Nanoparticles as a Fluid Loss Additive," in SPE International Conference on Oilfield Chemistry, 2019.
[14] J. V. Clavijo, L. J. Roldán, L. Valencia, S. H. Lopera, R. D. Zabala, J. C. Cárdenas, et al., "Influence of size and surface acidity of silica nanoparticles on inhibition of the formation damage by bentonite-free water-based drilling fluids. Part I: nanofluid design based on fluid-nanoparticle interaction," Advances in Natural Sciences: Nanoscience and Nanotechnology, vol. 10, p. 045020, 2019.
[15] A. E. Bayat, P. J. Moghanloo, A. Piroozian, and R. Rafati, "Experimental investigation of rheological and filtration properties of water-based drilling fluids in presence of various nanoparticles," Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 555, pp. 256-263, 2018.
[16] A. Parizad, K. Shahbazi, and A. A. Tanha, "SiO2 nanoparticle and KCl salt effects on filtration and thixotropical behavior of polymeric water based drilling fluid: With zeta potential and size analysis," Results in Physics, vol. 9, pp. 1656-1665, 2018.
[17] O. S. Guan, R. Gholami, A. Raza, M. Rabiei, N. Fakhari, V. Rasouli, et al., "A nano-particle based approach to improve filtration control of water based muds under high pressure high temperature conditions," Petroleum, 2018.
[18] A. Salih and H. Bilgesu, "Investigation of rheological and filtration properties of water-based drilling fluids using various anionic nanoparticles," in SPE Western regional meeting, 2017.
[19] I. V. Voronich, L. A. Gaidukov, and N. N. Mikhailov, "Fluid filtration to a horizontal well with variation in the parameters of the damage zone," Journal of Applied Mechanics and Technical Physics, vol. 52, pp. 608-614, 2011.
[20] J. Vargas, L. J. Roldán, S. H. Lopera, J. C. Cardenas, R. D. Zabala, C. A. Franco, et al., "Effect of Silica Nanoparticles on Thermal Stability in Bentonite Free Water-Based Drilling Fluids to Improve its Rheological and Filtration Properties After Aging Process," in Offshore Technology Conference Brasil, 2019.
[21] J. Hilhorst, V. Meester, E. Groeneveld, J. K. Dhont, and H. N. Lekkerkerker, "Structure and rheology of mixed suspensions of montmorillonite and silica nanoparticles," The Journal of Physical Chemistry B, vol. 118, pp. 11816-11825, 2014.
[22] A. R. Ismail, N. M. Rashid, M. Z. Jaafar, W. R. W. Sulaiman, and N. A. Buang, "Effect of nanomaterial on the rheology of drilling fluids," Journal of applied sciences, vol. 14, p. 1192, 2014.
[23] J. K. M. William, S. Ponmani, R. Samuel, R. Nagarajan, and J. S. Sangwai, "Effect of CuO and ZnO nanofluids in xanthan gum on thermal, electrical and high pressure rheology of water-based drilling fluids," Journal of Petroleum Science and Engineering, vol. 117, pp. 15-27, 2014.
[24] M. Zakaria, M. M. Husein, and G. Harland, "Novel nanoparticle-based drilling fluid with improved characteristics," in SPE international oilfield nanotechnology conference and exhibition, 2012.
[25] J. V. Clavijo, L. J. Roldán, L. Valencia, S. H. Lopera, R. D. Zabala, J. C. Cárdenas, et al., "Influence of size and surface acidity of silica nanoparticles on inhibition of
Chapter 4 117
the formation damage by bentonite-free water-based drilling fluids. Part II: dynamic filtration," Advances in Natural Sciences: Nanoscience and Nanotechnology, vol. 11, p. 015011, 2020.
[26] M. M. Barry, Y. Jung, J.-K. Lee, T. X. Phuoc, and M. K. Chyu, "Fluid filtration and rheological properties of nanoparticle additive and intercalated clay hybrid bentonite drilling fluids," Journal of Petroleum Science and Engineering, vol. 127, pp. 338-346, 2015.
[27] O. Mahmoud, H. A. Nasr-El-Din, Z. Vryzas, and V. C. Kelessidis, "Characterization of filter cake generated by nanoparticle-based drilling fluid for HP/HT applications," in SPE International Conference on Oilfield Chemistry, 2017.
[28] K. Song, Q. Wu, M. Li, S. Ren, L. Dong, X. Zhang, et al., "Water-based bentonite drilling fluids modified by novel biopolymer for minimizing fluid loss and formation damage," Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 507, pp. 58-66, 2016.
[29] G.-B. Cai, S.-F. Chen, L. Liu, J. Jiang, H.-B. Yao, A.-W. Xu, et al., "1, 3-Diamino-2-hydroxypropane-N, N, N′, N′-tetraacetic acid stabilized amorphous calcium carbonate: nucleation, transformation and crystal growth," CrystEngComm, vol. 12, pp. 234-241, 2010.
[30] N. Otsu, "A threshold selection method from gray-level histograms," IEEE transactions on systems, man, and cybernetics, vol. 9, pp. 62-66, 1979.
[31] A. Rabbani and S. Salehi, "Dynamic modeling of the formation damage and mud cake deposition using filtration theories coupled with SEM image processing," Journal of Natural Gas Science and Engineering, vol. 42, pp. 157-168, 2017.
[32] G. G. P. License, "GNU General Public License," Retrieved December, vol. 25, p. 2014, 1989.
[33] P. Klapetek, D. Necas, and C. Anderson, "Gwyddion user guide," Czech Metrology Institute, vol. 2007, p. 2009, 2004.
[34] R. C. da Luz, F. P. Fagundes, and R. d. C. Balaban, "Water-based drilling fluids: the contribution of xanthan gum and carboxymethylcellulose on filtration control," Chemical Papers, vol. 71, pp. 2365-2373, 2017.
[35] K. Backfolk, S. Lagerge, J. B. Rosenholm, and D. Eklund, "Aspects on the interaction between sodium carboxymethylcellulose and calcium carbonate and the relationship to specific site adsorption," Journal of colloid and interface science, vol. 248, pp. 5-12, 2002.
[36] Y. Kazemzadeh, M. Sharifi, M. Riazi, H. Rezvani, and M. Tabaei, "Potential effects of metal oxide/SiO2 nanocomposites in EOR processes at different pressures," Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 559, pp. 372-384, 2018.
[37] H. Rezvani, D. Panahpoori, M. Riazi, R. Parsaei, M. Tabaei, and F. B. Cortés, "A novel foam formulation by Al2O3/SiO2 nanoparticles for EOR applications: A mechanistic study," Journal of Molecular Liquids, vol. 304, p. 112730, 2020.
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Chapter 4 118
5. Effect of colloid filtration in porous media and the subsequent impairment of the rock permeability
Several challenges are present during oil well drilling operations. One is to generate a hole
with homogeneous geometry and a smooth, thin, and consistent filter cake [1] to ensure
the wellbore stability and avoid problems associated with induced formation damage [2, 3].
During overbalanced drilling, the drilling fluid is forced to penetrate through the porous
medium. First, the smallest particles and mud filtrate enters the region near the wellbore,
spurt loss. After, the larger particles are trapped in the pore throats associated with the
polymer acting as a retention barrier. Successively, these particles are deposited on the
rock surface, generating a filter cake [1, 4]. In this sense, permeability reduction during
drilling is usually caused by the solid particles and mud filtrate invasion into the porous
medium [5-7].
A solid particle in suspension is subjected to hydrodynamic forces such as drag, permeate,
lift, gravity, and electrostatic forces, which tend to deposit on the filter cake surface (chapter
4). The same forces act over the particles forced to enter into porous media [1]. An
equilibrium cake thickness during dynamic circulation is achieved when the particle forces
are higher than the tangential hydrodynamic force, it means. Electrostatic and permeate
forces attach, while drag, lifting, and gravitational forces detach them [2].
The electrostatic forces depend on the distance between particles (CaCO3), the maximum
when the distance is zero (dependent on water composition, pH, and temperature). The
interaction between particles and rock can also occur by several capture mechanisms, such
as attachment, size exclusion, bridging, etc. [3-5]. Permeate, lifting, and drag forces are
velocity-dependent (well flow conditions). However, all forces depend on the particle size.
Also, surface roughness filter cake increases tangential forces increasing the filter erosion
Chapter 5 120
[4]. The particle filtration and retention mechanisms cited above defines the filter cake build-
up and the permeability impairment.
Laboratory tests, such as coreflooding experiments, are the main approaches to investigate
physical and chemical effects on solid particle plugging. Several experiments have been
conducted to investigate SiO2 plugging effect under coreflooding micromodel [4] and shale
permeability apparatus [5]. The authors also determined filter cake/porous media
permeability using dynamic filtration even at different well angle inclinations [6]. Based on
their obtained results, various parameters such as NPs types, size, and concentration could
affect the filtration reduction through plugging the formation effectively. However, the
studies did not conclude or approximate the mechanism or SiO2 Nps-polymer-CaCO3-rock
interactions that allow the filter cake formation and the solid particle impact in the porous
media. Most studies have investigated the electrostatic forces involved. The application and
systematic evaluation of NPs in WBM to improve the filter cake properties and reduce the
filtration volume have not been evaluated under dynamic filtration, temperature, pressure
conditions to determine permeability reduction.
Therefore, this chapter aims at SiO2 NPs potential to improve filter cake formation under
porous media through coreflooding. NPs with the highest filtration reduction in the HPHT
and PPT tests were evaluated, SiC NPs now SiO2 NPs. Also, the SiO2 Nps-polymer-CaCO3
interactions allow the filter cake formation. The effluents obtained in the coreflooding test
were characterized to analyzed some NPs-formation fluids interaction. Effective oil, relative
permeability, and oil recovery curves were evaluated after the WBM injection across the
core face.
5.1. Experimental
5.1.1. Material
WBM and NPs employed are presented in chapter 1. Synthetic brine composed of sodium
chloride (NaCl, 99%, Sigma Aldrich, United States), magnesium chloride (MgCl2, 98%,
Sigma Aldrich, United States), potassium chloride (KCl, 99%, Sigma Aldrich, United
States), calcium chloride (CaCl2, 93%, Sigma Aldrich, United States), and sodium
bicarbonate (NaHCO3, 97%, Sigma Aldrich, United States). Colombian crude oil with 11.6º
Chapter 5 121
API, the viscosity of 6000 cP at 25°C, and asphaltene content of 16%. One sandstone core
from a Colombian field with a composition of 90% silica and 10% of clays, between them
chlorite (15%), kaolinite (60%), illite (5%), and slime size quartz (20%), was employed. The
core was cut into two representative pieces. The properties of the cores and the dynamic
filtration conditions are summarized in Table 5-1.
Table 5-1: Properties of the cores used in the displacement tests.
Property Core 1 Core 2
Length (cm) 6.95 6.63
Diameter (cm) 3.67 3.68
Pore volume (cm3) 9.81 9.5
Porosity (%) 13.3 13.5
Coreflooding conditions
Overburden pressure (psi) 3000
Pore pressure (psi) 1200
Temperature (°C) 87
Overbalance pressure (psi) 1770
5.1.2. Methods
• Preparation of synthetic brine
Synthetic brine for the coreflooding was prepared to add to 1.57g of NaCl, 0.05g of MgCl2,
0.08g of KCl, which was 0.37g of CaCl2, and it was 0.25g of NaHCO3, and 1.17g of BaSO4
to a 1L of deionized water and stirred for 1 hour.
• Preparation of the WBM
The formulation and preparation of the WBM can be found in Chapter 1 in Table 1-1.
• Coreflooding test
The schematic representation of the experimental setup for damage generation by drilling
fluid is shown in Figure 5-1. It consists mainly of a high flow pump (G Series/MACROY,
Chapter 5 122
Milton Roy, USA), a collector tank, and a specially in-lab-designed coreholder that allows a
mud transversal flow in the core face.
Figure 5-1: Experimental set up to damage generation by drilling fluid: 1) the coreholder, 2) the core, 3) the accumulator cylinders, 4) the high flow pump, 5) the back-pressure system, 6) the manometer, 7) commercial pump, 8) the collector tank, 9) valves and 10) drilling fluid [9].
Return permeability or formation damage by drilling fluid was evaluated according to the
protocol by Van der Zwaag [10]. Permeability curves were generated and compared before
and after the exposition of the drilling fluid. NPs performance was analyzed considering
three scenarios, namely: 1) baseline permeabilities, absolute permeability (Kabs), oil (Ko)
and water (Kw) effective permeabilities, the oil (Kro) and water (Krw) relative permeabilities,
as well as the oil recovery (OOIP); the scenario of the return permeabilities (Ko, Kw, Kro,
Krw, and OOIP) in the core exposed after the WBM in 2) the absence, and 3) the presence
of NPs.
Kabs of the cores were measured by injecting ten pore volumes of synthetic brine to induce
the original water-wet condition of the rock. The Ko was evaluated by injecting ten pore
volumes of crude oil until the pressure drop was stable and residual water saturation (Swr)
was reached. Also, a mixed wettability was induced and emulated the initial conditions of
the rock. Synthetic brine was injected until residual oil saturation (Sor) for the Kro, Krw, Kw,
and OOIP obtention. Then, cores were saturated again with crude oil until Swr. The system
was depressurized and transferred to the apparatus assembly in Figure 5-1. Drilling fluid
was circulated from the collector tank through the high flow pump to the coreholder for the
Chapter 5 123
drilling fluid damage generation. The coreholder was designed to allow the drilling fluid
circulation transversal to the coreface under temperature, shear rate, and overbalance
pressure, simulating the drilling fluid circulation between drill pipe and wellbore. The
dynamic filtration volume of the drilling fluid was measured each minute until the filtrate was
minimum to be measured. The mud filtrate invaded displaces the fluids that saturate the
core sample and is collected at the end of the back-pressure system; this is considered the
filtration volume. Subsequently, the Kro, Krw, Kw, and oil recovery were again evaluated,
injecting crude oil and water, respectively. Finally, crude oil was injected to determine the
Ko return to indicate the ultimate formation damage once the maximum fine particles and
mud filtrate were expelled from the core.
• Effluents evaluation
The crude oil effluents viscosity obtained after circulation of the drilling fluid in the presence
and absence of NPs and during the Ko return were performed using a rotational rheometer
(Kinexus Pro+, Malvern Instruments, United Kingdom) with a parallel plate geometry at a
gap of 1.00 mm, equipped with a Peltier cylinder cartridge for temperature control. Tests
were conducted at 87°C in a shear rate range of 1-100 s-1.
5.2. Results
Based on the obtained optimal concentration and thermal degradation results, the SiC NPs
at a fixed dosage of 0.1 wt.% were evaluated in the coreflooding tests due to their best
performance (see chapter 3). Now the terminology of SiC NPs will be SiO2 NPs. The Kabs
measured was 1374 ± 3 mD for both cores. The Kw curves are shown in Figure 5-2. The
Kw of the scenery without damage was 10 ± 2 mD. After exposure to the WBM without
NPs, a reduction of 70% was observed. The WBM with 0.1 wt.% SiO2 NPs only presented
a decrease of 45%. In the absence of NPs, polymer adsorbs onto the CaCO3 in the WBM
could enter and alter the rock wettability and block the pore throats, reducing the synthetic
brine mobility, whereas drilling fluid with NPs avoids this formation damage.
Chapter 5 124
Figure 5-2: Water effective permeability (Kw) as a function of the pore volumes injected (PVI) for the scenarios without damage and after the exposure of the WBM with and without 0.1 wt.% of SiO2 NPs.
The Ko curves of the different evaluated are presented in Figure 5-3. The displacement test
reproducibility was successfully achieved to ensure the same petrophysics properties. The
Ko for the undamaged scenario was 1232 ± 5 mD. After WBM in the absence of SIO2 NPs,
the Ko was reduced to 402 ± 5 mD. Formation damage degree by 67%. The Ko return was
169 ± 1 mD, increasing the damage by 18%. The total formation damage degree
corresponded to 76% compared with the undamaged scenario. A possible increment in the
crude oil effluent viscosity reduces the oil mobility (Please see Figure 5-4 below). For the
WBM with SiO2 NPs, the Ko decreased until 1030 ± 8 mD. Formation damage by 16%
compared with the undamaged scenario, attributed to the mud filtrate invasion reduction
and the effective filter cake formation. During the Ko return evaluation, the system
recovered the permeability to reach a value of 1157 ± 8 mD, suggesting that NPs avoid the
damage due to the blocking of pore throats. Still, it can also improve the rock and the
characteristics of the fluids.
Chapter 5 125
Figure 5-3: Oil effective permeability (Ko) as a function of the pore volumes injected (PVI) for scenarios without damage, after the exposure of the WBN with and without 0.1 wt.% of SiO2 NPs, and evaluation of Ko return.
Dynamic filtration curves during exposure of WBM in the absence and presence of 0.1 wt.%
SiO2 NPs are presented in Figure 5-4. The WBM without NPs filtrated 43 mL to the core
during an exposure time of 576 minutes. During the first 50 minutes, 50% of the total
filtration volume entered until the filter cake formation, which was still not impermeable,
allowed the filtration even after 500 minutes. In the presence of the SiO2 NPs, the filtration
volume was 9.8 mL in 80 minutes. The filter cake was formed quickly, and it was
impermeable since the first minutes of drilling circulation. The particle deposition was near
the core face due to the strong electrostatic attraction between the negatively charged
particles and the rock positive charge. Under dynamic filtration, the filter cake growth is
limited by erosion during circulation. Three stages can be defined during the dynamic
filtration process. The first one corresponds to the dynamic cake thickness. Solid particles
and mud filtrate invaded is very high. The filter cake thickness overgrows. For the second
stage, the filtration rate is reduced as time passes, the thickness filter cake erosion is
eventually equal to the growth. Finally, the thickness filter cake is constant, third stage [1].
The SiO2 NPs allowed a reduction of 77% in the mud filtrate regarding the system in the
absence of NPs. The filtration time was reduced by 87%, corroborating that NPs deposit in
the mudcake, fill the spaces between CaCO3 particles, and attach with the porous media.
The filter cake erosion is reduced during WBM circulation and reduces the permeability and
the porosity of the filter cake, as seen in the static tests. During the first minutes of drilling
fluid with NPs circulation, the curve slope is reduced, which means the thickness cake is
Chapter 5 126
constant. The shear rate did not erode the particles deposited; the attraction between
particles inside the filter cake is strong.
Lower solid particle and mud filtrate invasion indicate minor formation damage degrees, as
studied by Elkatatny [11, 12]. The Si-OH groups of the SiO2 NPs can potentially interact
with the silica groups of the sandstone rock surface. Various forces govern the adsorption
of NPs by electrostatic interactions [13], which may lead to the attachment of SiO2 NPs and
CaCO3 particles as the fluid is squeezed through the pores leading to reduced filter cake
porosity and permeability, better-plugging effect. The high percent reduction in the filtrate
volume suggests that the attachment of the SiO2 NPs and the CaCO3 particles to the pores
did not merely follow a physical mechanism, i.e., pore spacing filling. Rather selective
migration of the NPs and the CaCO3 took place due to the interactions between the SiO2
NPs-polymer-CaCO3-rock eluded to above. The molecular dynamic simulation suggested
that the polymer solution, composed of the xanthan gum and water, interacts the most with
sandstone, followed by SiO2 NPs and CaCO3. While the SiO2 NPs, interact the most with
rock, followed by CaCO3 and then polymer solution [14].
Figure 5-4: Cumulative filtration volume as a function of the time during the WBM circulation over the core face of sandstone core in the presence and absence of 0.1 wt.% SiO2 NPs.
Kro and Krw curves for undamaged scenario and after WBM circulation with and without
0.1 wt.% of SiO2 NPs are shown in Figure 5-5. The Kro and Krw values at Swr and Sor,
Chapter 5 127
called “endpoints”, were drastically reduced after the WBM exposure without NPs. For the
WBM with SiO2 NPs, a lower reduction in the endpoints was observed. The oil mobility was
not strongly affected, and thus, the porous media presented a high Ko value; somewhat,
the water mobility was reduced (see Figure 5-2 and Figure 5-3). An Swr increment and Sor
reduction were observed after WBM with SiO2 NPs pumped compared with the undamaged
scenario. SiO2 NPs act as a relative permeability modifier that retains the water in the
porous media increases water saturation, and favors crude oil mobility [15]. The opposite
was observed for the scenario of WBM without NPs. Within the wide range of saturation, in
the absence of NPs, the Kro and Krw were significantly reduced due to the higher solid
particles and mud filtrate invasion that plugged the rock, reducing the flow space reported
in Figure 5-4. The SiO2 NPs avoided the filtrate and particles invasion. Therefore, Kro and
Krw presented a lower reduction. Finally, Kro slope decreased, and Krw slope increased,
for the scenario without NPs, in the range of 0.27 to 0.71, and the crossover point moved
slightly to the left. These results showed that the oil lost, and the water gained mobility due
to a wettability change. For the scenario with NPs, the slopes and crossover points were
maintained. However, a wettability change is not discarded. The above analysis was
conducted to compare the damage scenario between WBM in the presence and absence
of NPs. The undamaged scenario was only a reference to demonstrate that the WBM with
NPs can inhibit the filtration volume and the formation damage and conserve the porous
media properties, which did not happen with the WBM without NPs.
Chapter 5 128
Figure 5-5: Oil relative permeability (Kro) and relative water permeability (Krw) as a function of the water saturation (Sw) for scenarios 1) without damage, 2) after the exposure of the drilling fluid without NPs, and (3) WBM with 0.1 wt.% of SiO2 NPs.
As a function of the pore volume injected (PVI), OOIP curves after WBM circulation with
and without SiO2 NPs are presented in Figure 5-6. The sandstone core after the WBM
without SiO2 NPs demonstrated an OOIP of 60%. WBM with SIO2 NPs recovered 66%,
more than a system without NPs. The flow channels were not obstructed by the solid
particles and the mud filtrate. Therefore, it is possible to recover this additional crude oil.
According to this result, adding NPs to WBM reduced formation damage by the invasion of
mud filtrate and solid particles. Also, NPs improve oil mobility, change rock wettability, and
reducing oil viscosity (discussion below). Table 5-2 summarizes some of the parameters
obtained during the displacement tests.
Chapter 5 129
Figure 5-6: Oil recovery factor (%OOIP) as a function of the pore volumes injected (PVI) for the scenarios after the exposure of the drilling fluid:1) without NPs, and 2) with 0.1 wt.% of SiO2 NPs.
Table 5-2: Summary parameters obtained during the displacement tests: Swr, Sor, and their respective reduction percentages.
Scenario Swr (%)
Change in
Swr (%) Sor (%)
Change in Sor
(%)
Undamaged 17 - 13 -
WBM 13 -76 29 - 113
WBM + 0.1 wt.% SiO2 23 + 35 23 - 169
Figure 5-7 shows the crude oil effluents viscosity obtained after the WBM circulation and
the Ko return. After the circulation of WBM with 0.1 wt.% of SiO2 NPs, a viscosity reduction
was observed. The effect was evaluated until 9 PVI. During the Ko return of the WBM with
SiO2 NPs, the crude returned to its original viscosity, verifying the impact of the SiO2 NPs
in the mud filtrate. Upon adding SiO2 NPs to the WBM, the maximum reduction was 28% at
the maximum shear rate (100 s-1). The effluent of the base mud during the Ko return
presented an increment due to an emulsion between mud filtrate, crude oil, and synthetic
brine. According to Betancur [16], SiO2 NPs with the smallest mean particle size, highest
total acidity, and highest surface area had the highest adsorptive capacities for n-C7. Hence,
the SiO2 NPs evaluated in this study could interact with the asphaltenes content presented
Chapter 5 130
in the heavy crude oil. Asphaltenes aggregate inhibition [17] and reduction of the
viscoelastic behavior studied by Taborda [18].
Figure 5-7: Viscosity of the crude oil effluents for the scenarios at a fixed shear rate of 100 s-1: 1) after the exposure of the drilling fluid with and without 0.1 wt.% of SiO2 NPs and 2) during the evaluation of Ko return, and 3) at different control point; 3, 6, and 9 PVI.
Some mechanisms influence permeability impairment during the drilling process. WBM
could alter the rock wettability but plug the pore throat due to the solid particles and the
mud filtrate invasion. The Swr increment near-wellbore causes capillary pressure
phenomena and modification of the permeability curves. Furthermore, this effect could be
higher with the invasion of polymer and adsorption onto the rock, plugging effect. The mud
filtrate expelled from the rock may take a considerable period before the permeability is
recovered [17, 18]. Finally, the invasion radius that reaches this permeability alteration
could affect the productivity of the well. SiO2 NPs used in this study reduced the filtration
volume, improved the filter cake characteristics, passed through it, and maximized wellbore
characteristics such as wettability and oil viscosity reduction, preventing formation damage
by drilling fluids. The higher return permeability can be attributed to several mechanisms:
lower solid particles invaded, wettability alteration, IFT reduction, and crude oil viscosity
reduction, some of them reduce the capillary forces and improve the formation fluids flow
through the pore channels. All conditions generated by the SiO2 NPs addition that promote
a considerable invasion radius reduction and the altered zoned had a favorable wettability
change and oil treatment. Once the NPs enter the formation through mud filtrate interact
Chapter 5 131
with the rock and formation fluids, the next chapter analyzes the microscopic phenomenon
involved.
NPs size and charge effect were confirmed, in this case, under dynamic conditions. Size
affects the stability of the dispersion; smaller sizes present excellent dispersion and could
avoid agglomeration. According to the charge, the repulsion forces are promoted caused
by the negative charge surface of NPs attributable to the silanol groups and the CaCO3
negative charge (electrical double layer). Also, the increase in the surface area caused by
the NPs size reduction means more space to interact with the polymer and improving the
steric repulsive forces (hydrogen bonding interactions). Once the filtration process starts,
the NPs can enter and stay in the space that is not occupied by the micrometric material
reducing the filter cake porosity and permeability, increasing the attractive forces between
CacO3, the distance of the deposited particle was reduced. The NPs were attached to the
porous media, higher affinity by covalent bonding through siloxane groups, and hydrogen
bonding interactions. Finally, the polymer can interact with the sandstones rock and reduce
the filtration volume (hydrogen bonding and electrostatic interactions). As mentioned
before, the order of interaction of NPs would be polymer<CaCO3<rock (see Figure 5-8).
Figure 5-8: Mechanism of interactions of the NPs-polymer system with porous media
Chapter 5 132
5.3. Partial conclusion
SiO2 NPs presented a physical mechanism occupying the empty spaces in the porous
media and retained in the porous surface due to the affinity between the silica groups of
the rock and the active sites of the SiO2 NPs. Hence, the SiO2 NPs could interact in the
following order with each item evaluated: Polymer < CaCO3 < rock. In the polymer case,
they interact stronger with the rock, CaCO3, and polymer solution in that order.
SiO2 NPs reduce the filtration volume by 77% and inhibit the Ko reduction by 76 %
compared with the WBM in the absence of the NPs. Crude oil viscosity was reduced up to
28% due to the NPs presence. As an additive WBM, SiO2 NPs effectively reduce fluid loss
and lower the formation damage.
The NPs evaluated in this study improve the WBM performance in terms of filtration volume
reduction and, consequently, the formation damage during drilling under dynamic
conditions. This study is expected to open a broader landscape about the use of
nanomaterials in the oil and gas industry to inhibit formation damage and improve
productivity during drilling operations.
5.4. References
[1] R. Caenn, H. C. H. Darley, and G. R. Gray, "Chapter 10 - Drilling Problems Related to Drilling Fluids," in Composition and Properties of Drilling and Completion Fluids (Seventh Edition), R. Caenn, H. C. H. Darley, and G. R. Gray, Eds., ed Boston: Gulf Professional Publishing, 2017, pp. 367-460.
[2] M. S. Al-Yasiri and W. T. Al-Sallami, "How the drilling fluids can be made more efficient by using nanomaterials," American Journal of Nano research and applications, vol. 3, pp. 41-45, 2015.
[3] M. Zakaria, M. M. Husein, and G. Harland, "Novel NPs-based drilling fluid with improved characteristics," in SPE international oilfield nanotechnology conference and exhibition, 2012.
[4] J. Dorman, I. Lakatos, G. Szentes, and A. Meidl, "Mitigation of formation damage and wellbore instability in unconventional reservoirs using improved particle size analysis and design of drilling fluids," in SPE European Formation Damage Conference and Exhibition, 2015.
[5] A. Suri and M. M. Sharma, "Strategies for sizing particles in drilling and completion fluids," SPE Journal, vol. 9, pp. 13-23, 2004.
[6] A. Abrams, "Mud design to minimize rock impairment due to particle invasion," Journal of petroleum technology, vol. 29, pp. 586-592, 1977.
[7] S. Vickers, M. Cowie, T. Jones, and A. J. Twynam, "A new methodology that surpasses current bridging theories to efficiently seal a varied pore throat
Chapter 5 133
distribution as found in natural reservoir formations," Wiertnictwo, Nafta, Gaz, vol. 23, pp. 501-515, 2006.
[8] D. Jiao and M. M. Sharma, "Mechanism of cake buildup in crossflow filtration of colloidal suspensions," Journal of Colloid and Interface Science, vol. 162, pp. 454-462, 1994.
[9] A. Kalantariasl and P. Bedrikovetsky, "Stabilization of external filter cake by colloidal forces in a “well–reservoir” system," Industrial & Engineering Chemistry Research, vol. 53, pp. 930-944, 2014.
[10] C. H. van der Zwaag, "Benchmarking the formation damage of drilling fluids," in SPE International Symposium and Exhibition on Formation Damage Control, 2004.
[11] S. Elkatatny, M. A. Mahmoud, and H. A. Nasr-El-Din, "Characterization of filter cake generated by water-based drilling fluids using CT scan," SPE Drilling & Completion, vol. 27, pp. 282-293, 2012.
[12] S. Elkatatny, M. Mahmoud, and H. A. Nasr-El-Din, "Filter cake properties of water-based drilling fluids under static and dynamic conditions using computed tomography scan," Journal of Energy Resources Technology, vol. 135, p. 042201, 2013.
[13] R. Abhishek, "Interaction of silica nanoparticles with chalk and sandstone minerals: Adsorption, fluid/rock interactions in the absence and presence of hydrocarbons," 2019.
[14] J. V. Clavijo, I. Moncayo-Riascos, M. Husein, S. H. Lopera, C. A. Franco, and F. B. Cortés, "Theoretical and Experimental Approach for Understanding the Interactions Among SiO2 Nanoparticles, CaCO3, and Xanthan Gum Components of Water-Based Mud," Energy & Fuels, 2021.
[15] E. A. Taborda, V. Alvarado, and F. B. Cortés, "Effect of SiO2-based nanofluids in the reduction of naphtha consumption for heavy and extra-heavy oils transport: Economic impacts on the Colombian market," Energy Conversion and Management, vol. 148, pp. 30-42, 2017/09/15/ 2017.
[16] S. Betancur, J. C. Carmona, N. N. Nassar, C. A. Franco, and F. B. Cortes, "Role of particle size and surface acidity of silica gel nanoparticles in inhibition of formation damage by asphaltene in oil reservoirs," Industrial & Engineering Chemistry Research, vol. 55, pp. 6122-6132, 2016.
[17] R. Abhishek, A. A. Hamouda, and I. Murzin, "Adsorption of silica nanoparticles and its synergistic effect on fluid/rock interactions during low salinity flooding in sandstones," Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 555, pp. 397-406, 2018.
[18] E. A. Taborda, C. A. Franco, M. A. Ruiz, V. Alvarado, and F. B. Cortés, "Experimental and Theoretical Study of Viscosity Reduction in Heavy Crude Oils by Addition of Nanoparticles," Energy and Fuels, vol. 31, pp. 1329-1338, 2017.
Chapter 5 134
6. Dual effect of SiO2 NPs on the improvement of the mud filtrate: wettability, interfacial tension, and fines migration retention
It had been possible to evaluate the NPs effect on the colloidal suspension stability and
later when they have been deposited. The SiO2 Nps-polymer-CacO3-rock interaction had
been established. However, determine what happens once the NPs enter into the formation
through the mud filtrate is necessary.
Mud filtrate and solid particle invasion near-wellbore during the drilling process and their
consequent induced formation damage are among the oil and gas industry problems [1-3].
The different mechanisms of damage due to mud filtrate can be associated with the polymer
adsorption into the rock and plugging [1], ionic incompatibility between filtrate and formation
water [4], aqueous filtrate trapping [5], wettability [6, 7], and pore-blocking effects [8] could
result from changes in the Swr [9, 10]. The formation of solid and fine particles could block
the pore throats and reduce the flow space [11, 12].
Reduction of the near-wellbore invasion of mud filtrate and mitigation of fines migration is
complicated by the design of the drilling fluids according to the selection of suitably sized
bridging material [13-16], filtration control additives [17], and filter cake development [18].
Simultaneously, the reservoir and formation fluid properties, particularly viscosity, interfacial
tension (IFT), and wettability, could change due to interactions between reservoir fluids, the
mud filtrate, and fine particles [10]. Recently, NPs have been employed to develop NPs-
based drilling fluid. NPs added act in the viscosity, filtration control, thermal and electrical
conductivity, and properties of the drilling fluid simultaneously [19-26]. However, these
studies do not consider the inhibition of the induced-formation damage. Moreover, it
Chapter 6 136
neglects the NPs-mud filtrate effect on porous media. Thus, this chapter aims to evaluate
the NPS invaded through the mud filtrate and rock and formation fluids interactions,
improved oil mobility, and migration fines control.
6.1. Experimental
6.1.1. Materials
Detailed information about employed NPs and WBM can be found in Chapter 1. For the oil-
wet disk, silica sand (Ottawa sand, U.S. Sieves 30 − 40 mesh), cement, and water were
used. An intermediate heavy crude, 23° API, and asphaltene content of 10.54% by weight
were used for oil-wet restoration.
6.1.2. Methods
Based on the results of rheological and filtration experiments, the optimal concentration of
NPs was selected to evaluate the performance of the mud filtrate obtained in their
respective filtration test to improve oil mobility and fines migration control. Mud filtrate from
the WBM with SiC NPs. The oil-wet disks were prepared by packing clean silica sand
(Ottawa sand, U.S. Sieves 30 − 40 mesh), cement, and water. Then, the disk was oil-wet
induced by asphaltene precipitation from an intermediate heavy crude oil. The disks were
submerged for 24 hours in the asphaltene solution and dried at 60°C for 16 hours.
• Contact angle, spontaneous imbibition test, and interfacial tension
measurements.
Oil-wet rock samples, representing the formation mineralogy, were immersed in the mud
filtrates with and without SIO2 NPs for 24 h at 25 °C. Then, the dynamic contact angle was
carried out through the sessile drop method using an Attention Theta optical tensiometer
(Biolin Scientific, Finland), the angle at 0 and 20 seconds was reported. A spontaneous
imbibition test of water into the oil-wet rock impregnated previously with the mud filtrate,
before dried at 70 °C overnight, was performed at room temperature, monitoring weight
changes in the system after being submerged. The imbibed water mass was recorded for
3.5 hours [27, 28]. Wettability changes were analyzed according to liquid/air/rock contact
angles formed in the surface samples treated with filtrate mud with and without NPs and
the differences between the imbibed mass. Finally, the IFT measure between crude
Chapter 6 137
oil/water formation and crude oil/mud filtrate with and without NPs was evaluated at 25°C
using a force tensiometer - K11 (Krüss, Germany). The same crude oil used for the oil-wet
induction was employed for the IFT measurements and the displacement test.
• Fines Retention Experimental Test.
Fines retention experimental tests were performed in synthetic porous media previously
impregnated with mud filtrate with and without NPs under atmospheric conditions. The
schematic representation of the experimental setup for fines retention experiments is shown
in Figure 6-1. The porous media were prepared with 70 g of Ottawa sand (Minercol S.A,
Colombia) (12-20 and 25-40 mesh) in a fraction mass of 50% ratio of each mesh. The
solution of fines was composed of a mass fraction of 0.2% kaolinite (𝐶𝑜). It is considered
the most problematic clay and the primary responsibility of the porous spaces plugging due
to its migration [29-31]. Hence, fines suspension was injected from the top and flowed
through the sand packed through gravity forces. The effluent was collected and passed
through filter paper to measure the quantity or concentration of fines retained. Before the
test, the sand bed was soaked for 24 hours with the mud filtrate with NPs to impregnate the
porous media. The filter paper is weighted each time a pore volume of fines suspension
has passed through the porous media, thus determining the fines retained using an
analytical balance (A & D company, United States) and obtaining the resultant
concentration fines (𝐶). The test finishes once the initial concentration is equal to the
effluent concentration (𝐶𝑜 = 𝐶) [30, 32].
Figure 6-1: Experimental setup to perform the fines retention experiments [32].
Chapter 6 138
6.2. Results
Generally, the mud filtrate invaded was considered rock contamination, altering the oil
saturation, wettability, capillary pressure, and other properties near-wellbore [12, 18].
However, this could change with the mud filtrate reduction and the enhancement of the mud
filtrate quality. The mud filtrate invaded with SiO2 NPs allows the oil mobility improvement
and migration fines control due to the SiO2 Np- rock interaction. So, the HPHT effluents with
the optimal concentration of 0.1wt.% were selected as they showed the highest filtration
reduction and improved filter cake thickness.
Figure 6-2 shows the drops of water placed onto the rock surface for a time of 0 and 20
seconds before and after mud filtrate soaking. The rock sample treated with the mud filtrate
in the absence of NPs showed an average contact angle for time 0 seconds of 127°, which
indicates a high oil-wet condition [33, 34]. However, the rock soaked with mud filtrate with
SiO2 NPs presented a reduction of 25% compared with the base scenario (mud filtrate
without NPs), reaching an average contact angle of 95°. After 20 seconds, the contact angle
was reduced to 67° for the rock sample treated with SiO2 NPs. Against the 120° for the
sample without NPs. The presence of SiO2 NPs favored water wettability. Whereas rock
samples treated with mud filtrate without NPs did not change the oil - wettability to water.
For oil droplets, contact angles after mud filtrate treatment without and with SiO2 NPs did
not change. Subsequently, spontaneous imbibition tests were performed with the rock
samples treated with mud filtrate and without NPs. The difference between the former test
is the available surface area in contact with the liquid; the water could enter through the
rock and interact with the porous interconnected.
Figure 6-2: Contact angles for the water/air/rock system treated with the mud filtrate: a) without NPs and b) with 0.1 wt.% SiC for 0 and 20 seconds.
t= 0 s
a) b)
Chapter 6 139
t= 20 s
Figure 6-3 compares the spontaneous imbibition of the rock samples treated with mud
filtrate in the absence of NPs and without and with 0.1 wt.% of SiO2 NPs. Fast-spontaneous
imbibition was observed for the rock with the mud filtrate with SiO2 NPs due to the capillary
pressure, which is the main driving force in spontaneous imbibition. The system is more
water-wet. These results are in agreement with the contact angle test. SiO2 NPs had an
affinity for the oil phase (oil-wet condition) that could be more easily adsorbed onto the
surface, making a thin film between the water drop and the solid surface, as reported in the
specialized literature [28, 35-37]. NPs cover the surface, inducing oil wettability change into
water preferences [28, 38]. NPs can spread along the surface by entering a structural
disjoining force (film). This NPs film acts higher repulsion force, separating the formation
fluids from the rock surface, especially the crude oil [39]. Also, the hydrophilic character of
the SiO2 NPs induces attraction to water molecules and repulse the crude oil. Also, NPs
could change the monovalent and divalent (Na+, K+, Ca2+, and Mg2+) with the rock surface
and alter the surface wettability, strong water-wet. The flow fluids in the pore channels
distribution are with the crude oil through the center and the water near the rock walls [40]
(see Figure 6-5).
Chapter 6 140
Figure 6-3: Spontaneous imbibition curves for sandstone cores soak with mud filtrate in the absence and presence of 0.1 wt.%. SiO2 NPs.
Regarding IFT, SiO2 NPs in the mud filtrate generated a reduction in IFT measurement from
25.4 ± 0.5 mN/m to 6.1 ± 0.3 mN/m, representing a reduction by 76% compared with the
crude oil/formation brine. In contrast, the mud filtrate without NPs did not represent a
significant change with IFT values of 26.9 ± 0.2 mN/m. The NPs create a layer at the crude
oil and brine interface, reducing the resistance between them, improving the oil mobility,
and decreasing the work needed to move oil droplets [41]. The fact that NPs decrease the
interfacial tension of the water-oil phase in which they are found can be explained
considering their hydrophilic behavior, preferentially partitions to the water phase, and does
not reside at the water-oil interface. NPs will adsorb on the interface, preferring water
molecules to reduce the area of the high-energy oil-water interface, the total energy of the
system be minimal. The repulsion forces are improved [42] (see Figure 6-5). Trapped oil
can be recovered if the ratio between the viscous and capillary forces, expressed in
literature as the capillary number Nc =µV/σcos(θ) [43], can be increased if the system
exhibits the minor flow restriction due to the reduction interfacial and wettability. Wettability
alteration and IFT reduction are two important mechanisms for enhanced oil recovery
(EOR), playing a dominant role in the possible oil mobility mechanisms.
Moreover, Figure 6-4 shows the breakthrough curve for the sand samples treated with mud
filtrate with and without SiO2 NPs at 0.1 wt.%. For the mud filtrate from WBM, the
Chapter 6 141
breakthrough curve shows the inherent retentive capacity to sand, which is considerably
lower than when impregnated with SiO2 NPs. These provide a greater fixate capacity of
fines on the sand. NPs influence on fine migration is given by reducing the zeta potential,
reducing the interaction energy between particles, pH change, and change in surface
roughness [44]. The fines retention could be that SiO2 NPs have a better affinity to clay
fines attaching the fines to sand grains. The attractive bonds between fine particles-rock
are strengthened by the NPs presence that had been previously adsorbed onto the surface.
NPs inhibit the fines migration by fixing them to the formation. [31, 45]. These results
correspond with the reported by Mora et al. [32]. Also, increasing surface roughness causes
the particle surface area and friction force to increase, attracting the fines particles to the
rock surface. NPs can change the surface roughness of fine particles (see Figure 6-5).
Figure 6-4: The breakthrough curve for the sand samples treated with mud filtrate in the absence and the presence of SiO2 NPs.
Chapter 6 142
Figure 6-5: Mechanisms of interactions of NPs once they enter the porous media through mud filtrate.
The WBM with SiO2 NPs reported a filtration volume reduction and rheological properties
improvement based on the obtained results. The mud filtrate that invaded the formation
could improve water-wettability tendency and IFT reduction and retain fine particles
released from the porous media or invaded from the drilling fluid. In this sense, the reduction
of IFT and water-wet tendency enhances the oil mobility and improves the oil recovery by
decreasing the work needed to move oil droplets through the pore throat [41]. Therefore,
the mud filtrate invaded will not represent other mechanisms of formation damage during
the drilling operation. Otherwise, this mud filtrate could improve the rock and formation
fluids properties.
6.3. Partial conclusions
SiO2 NPs presented contact angle reduction, 25%, IFT reduction 76%, and fine migration
control. NPs invaded through mud filtrate could generate and water-wettability rock and
retain the fines during the production time.
Chapter 6 143
6.4. References
[1] B. Peng, S. Peng, B. Long, Y. Miao, and W. Y. Guo, "Properties of high‐temperature‐resistant drilling fluids incorporating acrylamide/(acrylic acid)/(2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid) terpolymer and aluminum citrate as filtration control agents," Journal of Vinyl and Additive Technology, vol. 16, pp. 84-89, 2010.
[2] M. Aston, P. Mihalik, J. Tunbridge, and S. Clarke, "Towards zero fluid loss oil based muds," in SPE Annual Technical Conference and Exhibition, 2002.
[3] D. Jiao and M. M. Sharma, "Dynamic filtration of invert-emulsion muds," SPE drilling & completion, vol. 8, pp. 165-169, 1993.
[4] S. Gharat, J. Azar, and D. Teeters, "Effect of Incompatibilities Caused by Fluids Filtrates on Formation Properties," in SPE Formation Damage Control Symposium, 1994.
[5] D. B. Bennion, R. F. Bietz, F. B. Thomas, and M. P. Cimolai, "Reductions in the productivity of oil and low permeability gas reservoirs due to aqueous phase trapping," Journal of Canadian Petroleum Technology, vol. 33, 1994.
[6] D. Jia, J. Buckley, and N. Morrow, "Alteration of wettability by drilling mud filtrates," in Sept. 1994 SCA Symposium, Norway, 1994.
[7] G. Phelps, G. Stewart, and J. Peden, "The effect of filtrate invasion and formation wettability on repeat formation tester measurements," in European Petroleum Conference, 1984.
[8] A. Wojtanowicz, Z. Krilov, and J. Langlinais, "Experimental determination of formation damage pore blocking mechanisms," Journal of energy resources technology, vol. 110, pp. 34-42, 1988.
[9] R. Caenn, H. Darley, and G. Gray, "Chapter 10—Completion, reservoir drilling, workover, and packer fluids," Composition and properties of drilling and completion fluids, 6h edn. Gulf Professional Publishing, Boston, pp. 477-533, 2011.
[10] J. Argillier, A. Audibert, and D. Longeron, "Performance evaluation and formation damage potential of new water-based drilling formulas," SPE Drilling & Completion, vol. 14, pp. 266-273, 1999.
[11] R. Caenn, H. C. H. Darley, and G. R. Gray, "Chapter 7 - The Filtration Properties of Drilling Fluids11A glossary of notation used in this chapter will be found immediately following this chapter’s text," in Composition and Properties of Drilling and Completion Fluids (Seventh Edition), R. Caenn, H. C. H. Darley, and G. R. Gray, Eds., ed Boston: Gulf Professional Publishing, 2017, pp. 245-283.
[12] R. Caenn, H. C. H. Darley, and G. R. Gray, "Chapter 10 - Drilling Problems Related to Drilling Fluids," in Composition and Properties of Drilling and Completion Fluids (Seventh Edition), R. Caenn, H. C. H. Darley, and G. R. Gray, Eds., ed Boston: Gulf Professional Publishing, 2017, pp. 367-460.
[13] A. Suri and M. M. Sharma, "Strategies for sizing particles in drilling and completion fluids," SPE Journal, vol. 9, pp. 13-23, 2004.
[14] M. Dick, T. Heinz, C. Svoboda, and M. Aston, "Optimizing the selection of bridging particles for reservoir drilling fluids," in SPE international symposium on formation damage control, 2000.
[15] W. He and M. P. Stephens, "Bridging particle size distribution in drilling fluid and formation damage," in SPE European Formation Damage Conference, 2011.
[16] S. Vickers, M. Cowie, T. Jones, and A. J. Twynam, "A new methodology that surpasses current bridging theories to efficiently seal a varied pore throat
Chapter 6 144
distribution as found in natural reservoir formations," Wiertnictwo, Nafta, Gaz, vol. 23, pp. 501-515, 2006.
[17] H. C. Darley and G. R. Gray, Composition and properties of drilling and completion fluids: Gulf Professional Publishing, 1988.
[18] F. Civan, "Chapter 18-Drilling mud filtrate and solids invasion and mudcake formation, Reservoir Formation Damage," ed: Burlington: Gulf Professional Publishing, 2007.
[19] M. Al-Yasiri and D. Wen, "Gr-Al2O3 Nanoparticles based Multi-Functional Drilling Fluid," Industrial & Engineering Chemistry Research, 2019.
[20] B. J. A. Tarboush and M. M. Husein, "Adsorption of asphaltenes from heavy oil onto in situ prepared NiO nanoparticles," Journal of colloid and interface science, vol. 378, pp. 64-69, 2012.
[21] L. M. Corredor, M. M. Husein, and B. B. Maini, "Effect of hydrophobic and hydrophilic metal oxide nanoparticles on the performance of xanthan gum solutions for heavy oil recovery," Nanomaterials, vol. 9, p. 94, 2019.
[22] E. A. Taborda, V. Alvarado, and F. B. Cortés, "Effect of SiO2-based nanofluids in the reduction of naphtha consumption for heavy and extra-heavy oils transport: Economic impacts on the Colombian market," Energy Conversion and Management, vol. 148, pp. 30-42, 2017/09/15/ 2017.
[23] S. Perween, M. Beg, R. Shankar, S. Sharma, and A. Ranjan, "Effect of zinc titanate nanoparticles on rheological and filtration properties of water based drilling fluids," Journal of Petroleum Science and Engineering, vol. 170, pp. 844-857, 2018.
[24] L. J. Giraldo, M. A. Giraldo, S. Llanos, G. Maya, R. D. Zabala, N. N. Nassar, et al., "The effects of SiO2 nanoparticles on the thermal stability and rheological behavior of hydrolyzed polyacrylamide based polymeric solutions," Journal of Petroleum Science and Engineering, vol. 159, pp. 841-852, 2017.
[25] Z. Vryzas, L. Nalbandian, V. T. Zaspalis, and V. C. Kelessidis, "How different nanoparticles affect the rheological properties of aqueous Wyoming sodium bentonite suspensions," Journal of Petroleum Science and Engineering, vol. 173, pp. 941-954, 2019.
[26] M. Zakaria, M. M. Husein, and G. Harland, "Novel nanoparticle-based drilling fluid with improved characteristics," in SPE international oilfield nanotechnology conference and exhibition, 2012.
[27] M. Franco-Aguirre, R. D. Zabala, S. H. Lopera, C. A. Franco, and F. B. Cortés, "Interaction of anionic surfactant-nanoparticles for gas-Wettability alteration of sandstone in tight gas-condensate reservoirs," Journal of Natural Gas Science and Engineering, vol. 51, pp. 53-64, 2018.
[28] J. Giraldo, P. Benjumea, S. Lopera, F. B. Cortes, and M. A. Ruiz, "Wettability alteration of sandstone cores by alumina-based nanofluids," Energy & Fuels, vol. 27, pp. 3659-3665, 2013.
[29] X. Liu and F. Civan, "Formation damage and skin factor due to filter cake formation and fines migration in the near-wellbore region," in SPE formation damage control symposium, 1994.
[30] C. Céspedes Chávarro, "Desarrollo de un nanofluido para la estabilización de finos de la formación barco del campo Cupiagua," Universidad Nacional de Colombia-Sede Medellín.
[31] C. Franco Ariza, F. Cortés, D. Arias-Madrid, E. Taborda, N. Ospina, R. Zabala, et al., "Inhibition of the formation damge due to fine migration on low-permeability reservoirs of sandstone using silica-based nanfluids: from laboratory to a successful field trial.," ed, 2018, p. 231.
Chapter 6 145
[32] C. M. Mera, C. A. F. Ariza, and F. B. Cortés, "Uso de nanopartículas de sílice para la estabilización de finos en lechos empacados de arena Ottawa," Informador técnico, vol. 77, pp. 27-34, 2013.
[33] W. Anderson, "Wettability literature survey-part 2: Wettability measurement," Journal of petroleum technology, vol. 38, pp. 1,246-1,262, 1986.
[34] A. Cassie and S. Baxter, "Wettability of porous surfaces," Transactions of the Faraday society, vol. 40, pp. 546-551, 1944.
[35] K. Kondiparty, A. D. Nikolov, D. Wasan, and K.-L. Liu, "Dynamic spreading of nanofluids on solids. Part I: experimental," Langmuir, vol. 28, pp. 14618-14623, 2012.
[36] S. Al-Anssari, S. Wang, A. Barifcani, M. Lebedev, and S. Iglauer, "Effect of temperature and SiO2 nanoparticle size on wettability alteration of oil-wet calcite," Fuel, vol. 206, pp. 34-42, 2017.
[37] H. Jang, W. Lee, and J. Lee, "Nanoparticle Dispersion with Surface-modified Silica Nanoparticles and Its Effect on the Wettability Alteration of Carbonate Rocks," Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2018.
[38] C. Franco, E. Patiño, P. Benjumea, M. A. Ruiz, and F. B. Cortés, "Kinetic and thermodynamic equilibrium of asphaltenes sorption onto nanoparticles of nickel oxide supported on nanoparticulated alumina," Fuel, vol. 105, pp. 408-414, 2013.
[39] H. Eltoum, Y.-L. Yang, and J.-R. Hou, "The effect of nanoparticles on reservoir wettability alteration: a critical review," Petroleum Science, vol. 18, pp. 136-153, 2021.
[40] L. Hendraningrat, S. Li, and O. Torsæter, "Effect of some parameters influencing enhanced oil recovery process using silica nanoparticles: an experimental investigation," in SPE Reservoir Characterization and Simulation Conference and Exhibition, 2013.
[41] A. Roustaei, S. Saffarzadeh, and M. Mohammadi, "An evaluation of modified silica nanoparticles’ efficiency in enhancing oil recovery of light and intermediate oil reservoirs," Egyptian Journal of Petroleum, vol. 22, pp. 427-433, 2013.
[42] H. Fan, D. E. Resasco, and A. Striolo, "Amphiphilic silica nanoparticles at the decane− water interface: Insights from atomistic simulations," Langmuir, vol. 27, pp. 5264-5274, 2011.
[43] L. J. Giraldo, J. Gallego, J. P. Villegas, C. A. Franco, and F. B. Cortés, "Enhanced waterflooding with NiO/SiO2 0-D Janus nanoparticles at low concentration," Journal of Petroleum Science and Engineering, vol. 174, pp. 40-48, 2019.
[44] A. Madadizadeh, A. Sadeghein, and S. Riahi, "The use of nanotechnology to prevent and mitigate fine migration: a comprehensive review," Reviews in Chemical Engineering, 2020.
[45] N. C. Ogolo, O. A. Olafuyi, and M. Onyekonwu, "Effect of nanoparticles on migrating fines in formations," in SPE International Oilfield Nanotechnology Conference and Exhibition, 2012.
Chapter 7 146
7. Field application: lessons learned
Despite the experimental developments achieved so far, there are few applications of NPs
for drilling oil wells in the field. Borisov et al. used calcium-based NPs (CNP) for field
implementation due to their excellent performance in laboratory fluid loss experiments.
Large-scale field test results indicated that total mud losses while drilling were 27% lower
than conventional drilling fluids. This loss prevention is within the range observed in the
laboratory [1].
In this way, there is an excellent opportunity to develop NPs-based drilling fluids, which
improve the WBM properties reducing the filtration volume and the formation damage
degree. Additionally, no field applications have been reported in Colombian wells.
Therefore, this chapter presented the field-level performance of an
experimentally designed drilling nanofluid for an Ocelote field to mitigate the formation
damage according to the theoretical and experimental investigation developed in this
thesis. The optimal NPs concentration is selected, and subsequently, it is tuned with the
carrier fluid. The field application scheme was designed, and its performance was evaluated
by evaluating the invasion radius, the productivity index, among other production factors
that allow determining the effect of the NPs in the well to be drilled. The described
comparison contemplates the evaluation following parameters between two homologous
wells, Well A and Well B.
7.1. Experimental
The methodology exposed below accounts for the experimental test that will better
understand the phenomena related to the NPs/carrier fluid used in the drilling fluid
formulation and the field application procedures.
Chapter 7 148
7.1.1. Material
In this work, metallic oxide commercial NPs (NP1) were used. Simultaneously, the service
company (Petroraza S.A.S) provided a commercial nanofluid (NP1/carrier fluid). The WBM
employed in this application had a conventional composition of a drilling fluid used in the
Ocelote field: NaOH, water, xanthan gum, starch, CaCO3, lubricant, and surfactant. The
design and characteristics of NPs cannot be replied to.
7.1.2. Methods
• Drilling fluid preparation and characterization in laboratory
The WBM was prepared by mixing each additive for 10 min in the mixer (Hamilton Beach,
USA) at low speed in the order that they are mentioned in Table 7-1. The NPs/carrier fluid
effect was evaluated by analyzing the rheological, HPHT, and PPT filtration properties
following the procedure described in Section 1.1.5.
Table 7-1: Drilling fluid formulation for the field application
Additive Function
Concentration (lbs.bbl-1) Mixing order
Min Max Lab Well A Well B
NaOH pH control 0.3 0.5 pH 9.5 6 7
Starch Filtration control 4.5 5.5 5.0 1 1
Lubricant
Swelling inhibitor
and ROP
enhancement
4.0 4.0 1.0 7 8
Xanthan gum Viscosifying 1.0 1.5 1.5 2 2
NP1 Filtration control 1% V/V* 1%
V/V* 1% V/V* - 3
CaCO3 M200 Bridging material 10 10 10 4
Chapter 7 149
CaCO3 M325 20 20 20 5
CaCO3 M1200 5 5 5 6
Surfactant Surfactant 1500
ppm
2000
ppm
2000
ppm 8 9
* To obtain a concentration of 500 mg. L-1 of solid NPs from a concentrated suspension of
50,000 ppm
• Upscaling and Field Test
The pilot was carried in August 2020 in two development wells in the Ocelote field whose
target formation is Carbonera formation, a thick succession of interbedded, sand-rich
members (Carbonera members 1, 3, 5, and 7) and muddy members (Carbonera members
2, 4, 6, and 8) [2]. In the study area, oil and gas producing intervals correspond to the
Carbonera Member 7 (C7). Well A was drilled with a conventional WBM in the interval depth
between 4275 and 4315 ft. Well B used the WBM with the nanofluid evaluated
experimentally to drilled the interval 4760 and 4840 ft. Well A and B were drilled in two
sections, the section of 9 5/8 in and 7 in. The first section was drilling with an overburden
fluid with a density between 8.5 and 8.6 ppg. After that, a conductor pipe was cementing
for environmental regulation. For the Second section, a BFWBM was employed with a
density interval of 8.6 - 9.1 ppg. According to the well, the BFWBM was changed 200 ft
before C7 for the WBM with and without NPs. A casing liner of 7 in was placed into the well
and cementing. Finally, the assembly of downhole tubular and equipment to enable safe
and efficient production was done in member C7: cement logging, perforating, sand control
equipment, and the electric downhole pump. Table 7-2 summarizes the wellbore diagram
for Well A and B. Well A was a counterpart to Well B. They produce from the same
stratigraphic unit and are located in the same area.
Chapter 7 150
Table 7-2: Wellbore diagram and drilling fluids
Formation Interval Depth (ft) Casing liner Hole (in) Mud (ppg)
620
9 5/8 in
Shoe
Well A: 620 ft
Well B: 700 ft
12 1/4
8.5 – 8.6
Overburden
fluid
4800
7 in
Shoe
Well A:4330 ft
Well B:4800 ft
8 1/2
8.6 – 9.1
Bentonite-
based fluid
8.8 – 8.9
WBM
For the drilling of well A, 480 Bbls of WBM were prepared following additive addition and
concentration scheme presented in Table 7-1, without NP1 carrier fluid. For the WBM of
well B, 520 Bbls were prepared due to the greater depth and C7 thickness for the formation.
The addition of the additives and concentration scheme is presented in Table 7-1.
Additionally, monitoring of the pH was performed after the addition of NP1; the acid
character could decrease the pH and affect the colloidal stability of the WBM. Nanofluid
addition was slow after the polymer hydration with the previous agitation and above the
tanks to ensure good NPs-WBM components interaction. Strengthen the viscoelastic
structure and favors the steric hindrance at the time of addition of CaCO3. Some of the
operative conditions are summarized in Table 7-3. Once drilling starts, the procedure for
changing the BFWBM to WBM with or without NPs depending on the well was as follows
(see Figure 7-1):
Chapter 7 151
1. Before C6 top, the BFWBM return was stock into the return tank through the by-
pass channel, and from there, the fluid was pumped to disposal.
2. Previously, the WBM with NP1 was mixed in the reserve tank and is transferred to
the suction tank.
3. 200 ft before reaching C7, a viscous pellet is pumped from the pill tank in which it
was mixed previously to avoid mixing between BFWBM and WBM and start drilling
the C7 formation with WBM.
4. Subsequently, the WBM with or without NP1 was pumping to the well from the
suction tank. During the C6 and C7 formation (200 ft), the WBM was disposed of
due to mixing with the viscous pellet.
5. Finally, when the WBM circulation is verified thoroughly in shakers, the fluid is
directed through the by-pass channel to the suction tank and drilled in a short circuit.
During the short circuit, the drilling fluid will only pass through the Shakers.
Table 7-3: Drilling conditions during interval C7.
Well A Well B
Thickness (ft) 170 200
Volume (Bbls) 480 520
Caudal (gpm) 400 400
Total pressure loss (x10 psi) 172 184
Drilling time (min) 66 87
Effective ROP (ft/h) 188 169
Average ROP (ft/h) 92 65
Chapter 7 152
Figure 7-1: Removal section and tank arrangement for preparation and circulation of the
WBM with and without NPs
• Procedures for Field Testing
Drilling fluid performance: Three WBM samples were verified during drilling operation in
three-time intervals. Properties such as rheology, filtration LPLT, HPHT, and PPT, solid
particle size, among others, were analyzed based on the procedures exposed in section
1.1.5.
Invasion diameter calculation by electrical logging. Considered the different depths of
investigation of resistivity logging and the difference between the salinity of the WBM and
formation brine, the invasion profile was defined as the difference between them. The
objective is to compare the invasion profile for the well without NPs and the well where the
technology is provided, compare the values in the formation of interest (C7), and quantify
the difference percentage.
Stabilized time of reservoir production conditions: During the production time of the
Ocelote field, some wells take longer to produce completion fluids. These cases have been
Chapter 7 153
associated with deficiencies in filtration control. Given the above, the time it takes to make
the reservoir fluids, and the volumes produced before producing the reservoir fluids will be
calculated. The pipe capacities were considered.
Productivity index (PI): The initial productivity index will be compared normalizing by feet
of open formation between the comparison wells. The frequency changes and draw-down
will be the same for both wells.
Solid content: Monitor daily solid production for 15 days. Five gallons of wellhead sample
was taken after completion fluids production and other samples after eight days for X-ray
diffraction (XRD) and particle size distribution (PSD) evaluation of the solids that can be
recovered (if recovery is feasible).
7.2. Results
7.2.1. Laboratory evaluation
The experimental evaluation in the laboratory consisted of determining the optimal
concentration of NP1. Subsequently, the nanofluid was tested, employing the concentration
to be used in the field. Finally, the bridging capacity of the drilling fluid was evaluated in
PPT tests. All tests were executed before and after the dynamic aging processes.
The optimal NPs concentration: The HPHT filtration results for the WBM before and after
aging varying the NP1 concentration are presented in Table 7-4. A discrete reduction in the
filtration volume was observed for the concentration of 0.05 wt.%, even for fresh and
degraded WBM. Filter cake thickness reduction was more representative, 15% and 33%
before and after aging, respectively, for the optimal concentration of 0.05 wt.%.
Table 7-4: HPHT filtration for the WBM before and after heat treatment varying the NP1
concentration.
Before heat treatment After heat treatment
WBM
NP1 (wt.%)
WBM
NP1 (wt.%)
0.03 0.05 0.1 0.03 0.05 0.1
𝑽𝒇 (mL) 13.6 14.0 13.2 12.8 13.6 26.0 13.2 18
Chapter 7 154
% 𝑽𝒇 reduc. - 2.9 -2.9 -5.9 - 91.2 -2.9 32.4
𝒉𝒎𝒄 (mm) 2.6 2.1 2.2 1.2 2.1 3 1.4 1.9
% 𝒉𝒎𝒄 reduc. - -19.2 -15.4 -53.8 - 42.9 -33.3 -9.5
Figure 7-2 present the filter cake photographic record after heat treatment of the WBM
without and with 0.05 wt.% of NP1. As well as what has been discussed through this thesis,
greater consistency and thickness reduction were observed. It was possible to determine
the optimal concentration, 0.05 wt.%, presenting the highest percentages of filtration
volume and thickness reduction for both fresh and degraded WBM. The optimal
concentration was selected to evaluate its synergy with the carrier fluid and its subsequent
evaluation in alloxite disks to determine its bridging properties.
Figure 7-2: Photographic record of the filter cake (HPHT test) after thermal degradation: a)
WBM without NPs and b) WBM with 0.05 wt.% NP1.
Carrier fluid evaluation: The addition of NPs to the WBM in the field should be dispersed
in a carrier fluid, given its easy application, avoiding the particles volatility in the air, and
complying with safety and work regulations. The NPs stability in the WBM and the effect of
the carrier fluid on the WBM properties were evaluated. Table 7-5 presents HPHT filtration
Chapter 7 155
properties using carrier fluid (50,000 mg.L-1) and water (500 mg.L-1) for fresh and degraded
WBM in the presence and absence of NP1. A more significant reduction was observed for
the filtration volume and the thickness filter cake, 5 and 50%, respectively, when water was
used as the carrier fluid of the NP1 for fresh mud. Additionally, the filtration volume was
reduced by 18% after heat treatment and a reduction of 66% for the filter cake thickness.
The filtration volume and filter cake thickness increased for the commercial carrier fluid for
both fresh and degraded mud, the effect after degradation being more noticeable. This
effect could be related to the colloidal suspension destabilization due to the saturated
carrier fluid with NP1. A surfactant is present in the formulation to favors the NPs
dispersions, but it is unfavorable for the WBM stability. It was not possible to tune the carrier
fluid with NP1. Figure 7-3 shows the filter cake photographs for the filter cake after heat
treatment of the WBM without NPs, with the NP1/carrier fluid, and NP1/water. Over a
consistent and low thickness cake is observed.
For the field application, the NP1 addition after polymer hydration and at the end of the
formulation were evaluated. Although the results so far indicate no difference in the order
of addition, there were changes according to the carrier fluid type. The NPs previously
hydrated, dispersed, and homogenized in an aqueous medium increased their affinity to
water molecules reducing the NPs-polymer interaction. The aggregate size (NPs-polymer)
decreases [3], allowing a more significant NPs-CaCO3 interaction. Therefore, viscosity
changes are not evident (see the section below), but if in the filter cake properties. If the
NPs-CaCO3 interaction increases instead of the polymer, we are strictly improving the filter
cake properties, permeability, and porosity.
Table 7-5: HPHT filtration for the WBM before and after heat treatment: a) WBM without
NP1, b) WBM with 0.05 wt.% NP1/carrier fluid, and c) WBM with 0.05 wt.% NP1/water.
Before heat treatment After heat treatment
WBM NP1/Carrier
fluid NP1/Water WBM
NP1/Carrier
fluid NP1/Water
(mL) 13.6 15.1 12.4 13.6 11.2 20.5
% reduction - 13.2 -8.8 - -17.6 83.0
Chapter 7 156
(mm) 2.6 3.5 1.3 2.1 1.3 3.5
% reduction - 34.6 -50.0 - -38.1 66.7
Figure 7-3: Photographic record of the filter cake (HPHT) after heat treatment: a) WBM
without NP1, b) WBM with 0.05 wt.% NP1/carrier fluid, and c) WBM with 0.05 wt.%
NP1/water
PPT filtration test: Finally, the optimal concentration and carrier fluid, 0.05 wt.%
NP1/water, from the HPHT static filtration results were evaluated in the PPT tests on 20 µm
alloxite disks before and after heat treatment see Table 7-6. Spurt loss and total filtration
volume were observed for the WBM in the presence of NP1/water. The nanofluid effect
became more noticeable after heat treatment with 82 and 36% reductions in spurt loss and
total filtration volume, respectively. Finally, Figure 7-4 shows the filter cake (PPT test) after
heat treatment of WBM without and with 0.05 wt.% NP1/water. The filter cake obtained was
Chapter 7 157
more consistent with less thickness and more compact. In this way, it was possible to select
the best concentration and carrier fluid applied in the field. Also, regardless of the order of
addition, it was defined that the most convenient is the addition of nanofluid after polymers
hydration with adequate monitoring of the pH value during the drilling process.
Table 7-6: PPT filtration for the WBM before and after heat treatment: a) WBM without NP1
and b) WBM with 0.05 wt.% NP1/water.
Before heat treatment After heat treatment
WBM NP1/Water WBM NP1/Water
Spurt loss 4,5 2,8 2,9 0,5
% reduction - −37 - −82
Total filtration
volume (mL) 15,5 13,0 12,7 8,1
% reduction - - 16 - −36
(mm) 1,4 1,1 1,3 1,1
% reduction - −19 - −10
Figure 7-4: Photographic record of the filter cake (PPT) after heat treatment: a) WBM
without NP1 and b) WBM with 0.05 wt.% NP1/water
Chapter 7 158
Rheological behavior: PV, YP, and Gel of WBM without and with NP1 and NP1/water
before and after heat treatment are presented in Table 7-7. Increment less than 6% in the
yield point was observed in the presence of NP1/water for fresh WBM. There was no
evidence of a significant effect of NP1 on the other rheological properties. These results
are consistent with the results of previous sections. However, in the presence of NP1 the
PV, and YP were improved even with the carrier fluid. Once again, NPs reduce the WBM
heat treatment.
Table 7-7: Rheological properties before and after heat treatment: a) WBM without NP1,
b) WBM with 0.05 wt.% NP1, and c) WBM with 0.05 wt.% NP1/water.
Before heat treatment After heat treatment
WBM 0.05%
NP1
0.05%
NP1/water WBM
0.05%
NP1
0.05%
NP1/water
VP (cP) 15.9 15.7 15.8 14.6 22.4 23.5
YP
(lb/100ft2) 25.9 25.3 26.4 17 21 20
Gel 10''/10' 5/8 5/7 5/7 5/7 5/7 5/7
7.2.2. Field application
Drilling fluid performance: Table 7-8 shows the properties of the WBM samples taken in
the field. No significant differences are observed in the rheological and filtration properties
between the two formulations. The effect of NPs in the WBM was not observed at the field
scale. Among the assumptions was the increase in the lubricant in the field application
compared to laboratory evaluation. Variations in the drilling fluid formulation could generate
changes in the stability and performance of the NPs. Also, an experimental assessment did
not consider additive sensibilization; in the field, the addition is not strictly exact as it is
evaluated in the laboratory. Additionally, the water quality used for the WBM preparation in
the field application could alter the properties of the NPs due to the presence of salt content
that was not evaluated in the laboratory.
Chapter 7 159
Table 7-8: Summary of the WBM properties evaluated in the field for the initial,
homogenized, and final stages.
Property
Initial stage Homogenized stage Final stage
WBM NP1/water WBM NP1/water WBM NP1/water
Density (ppg) 8,9 8.9 8,9 8.9 8,9 8.9
pH 9,5 9.8 9,6 9.8 10,2 10.8
Fann θ600, 300, 200,
100, 6, and 3
46/34/27/21/
9/8
42/32/26/20/
10/9
46/34/28/22
/9/8
40/30/25/20/
8/7
45/34/27/21/
9/8
45/34/26/22/
10/9
PV (cP) 12 10 12 10 11 11
YP (lb.100 ft-2) 22 22 22 20 23 23
Gel (10/10/30)
(lb.100 ft-2) 8/10/14 9/9/10 8/10/14 8/10/14 8/10/14 9/12/16
API filtrate (mL) 4,6 4.6 4,5 4.4 4,8 4.8
𝒉𝒎𝒄 (1/32") 1 1 1 1 1 1
Filtrate PPT
(Spurt loss/VT)
(mL)
0.8/10.6 1.4/9.6 0.8 / 10.8 1.8/9.8 2/12 2.0/11.0
Filtrate HTHP
(mL) 10,2 10.8 10,4 11.2 11,6 10.8
Invasion radius: The invasion profile differed between the resistivity curves at the different
evaluation depths. Deep resistivity of 12 in (red line) corresponds to the formation of brine.
Medium resistivity (blue line) of 6 and 3 in. Shallow resistivity (green line) of 1 and 2 in. The
last two correspond to the mixing between the formation brine and mud filtrate. Given the
above, it was inferred as a high fluid invasion when there is a pronounced separation
Chapter 7 160
between resistivity curves. Simultaneously, a low or no invasion corresponds to a record
without separation between curves.
Figure 7-5 shows the well-drilled invasion profile with WBM without NPs, well A, and for
the well-drilled with WBM and NP1/water. Well A did not present an invasion radius
and control of the mud filtrate. For well B, the invasion was 8.5 in, which represents a
lower value than those obtained in previous drilling campaigns, 12 in, but it did not denote
the performance of the WBM without NPs. Notably, there is a slight difference in lithology
since the sand from well B compared to that from well A is thicker and a little cleaner,
which is why a more significant invasion was expected, as observed in the gamma-ray log
as reported in
Table 7-9.
Figure 7-5: Invasion profile for the: a) Wells A and b) Well B.
Chapter 7 161
Table 7-9: Petrophysical properties for Well A and B through well log analysis.
Well Zones Net (ft) VSH (%) φ (%) Sw (%) K mD Resistivity
(ohm.m)
GR
(gAPI)
A
C7A 2 6.3 30.8 51 697 80 69
C7B 4 7.9 22.1 53 603 133 49.4
B
C7A 4 4 27 46 402 56 57
C7B 4 7 23 54 853 77 40
Stabilized time of reservoir production. After drilling, Wells A and B were close due to
biosafety measures and protocols associated with a pandemic condition caused by COVID-
19. Well A had a cleanup time of 8 days compared to 10–15 days of the wells drilled in the
region. There was evidence of an improvement in the wells cleaning after drilling. However,
for Well B, the time could not be quantified in the same way because formation damage
was generated by fines migration that prevented testing of the well post-drilling. Due to the
draw-down exerted in the well B and the abundant presence of solids in the crude oil sample
from Well A, a strong plugging was presumed by fines migration and accommodation of
fines in Well B corresponding to formation damage.
PI evaluation. Figure 7-6 shows the record of Wells A and B of the barrels of fluid per day
(BFPD), basic sediment and water (BSW), barrel of oil per day (BOPD), frequency of
electric downhole pump (ESP), and pressure intake pump (PIP). The area in which Well A
and B were drilled exhibits a low PI due to the low-quality of the rock compared to the other
Ocelote field wells. During the first days of production, Well A has a normalized PI of 0.5
Bbbl.(d.psi)−1 consistent with the area petrophysics, low BSW, and production of 200 barrels
of fluid per day (BOPD). Regarding Well B showed a PI of 0.1 Bbbl.(d.psi)−1, there was no
stable production from the well due to formation damage identified. Nowadays, Well B had
a PI of 0.5 Bbbl.(d.psi)−1 with 41 BOPD after well intervention; see Figure 7-6 and Figure
7-7.
Chapter 7 162
Figure 7-6: Barrels of fluid per day (BFPD), basic sediment and water (BSW), barrel of oil per day (BOPD), frequency of electric downhole pump (ESP), and pressure intake pump (PIP) for the: a) Wells A and b) Well B.
Figure 7-7: Actual BFPD, BOPD, BSW, and PI for Wells A and B (13/02/2021).
Chapter 7 163
Solid content. Table 7-10 shows solid contents for Wells A and B, which exhibited similar
solid production behavior with a maximum concentration of 3.94 PTB. There is no marked
difference in terms of the solid output after the well started-up, so it is inferred that with the
WBM with NP1/Water, there was evidence of fines migration retention in the medium.
Table 7-10: Solid content Well A and B during production.
Well A Well B
Sample Date Time Solids PTB Sample Date Time Solids PTB
24/08/2020 15:00 1.36 24/08/2020 15:00 1.05
25/08/2020 3:00 3.94 25/08/2020 3:00 2.28
25/08/2020 15:00 0.69 25/08/2020 15:00 1.44
26/08/2020 3:00 0.24 26/08/2020 3:00 0.37
26/08/2020 15:00 0.15 26/08/2020 15:00 0.87
Well B hypothesis was related to fines migration and plugging, either from the gravel pack
or from the well. The accumulation of solids that cannot be lifted due to the low flow rate is
not ruled out. The PIs and productivities of the zones are congruent with neighboring wells.
However, after the increase in draw-down performed in Well B, there was a substantial
decrease in it, in line with the effects of fines plugging of fines near the wellbore.
7.2.3. Lesson learned and recommendations
• The interaction of NP1 with the WBM components such as lubricants, surfactants,
among others, should be evaluated in greater detail. Changes in the colloidal
suspension stability could occur, which can generate considerable alterations at the
field scale.
• There are high uncertainties in the key performance indicators (KPI) due to the
multiple variables involved in drilling, reservoir conditions, and post-drilling startup.
These contingencies must be included in the analysis before the execution of a new
Chapter 7 164
pilot. Adequate control is required at post-drilling startup of the well to prevent
premature formation damage.
• The additive concentrations in the field are not exact but are managed in a minimum
and maximum range. It is necessary to include such sensitivity in the evaluation of
drilling fluids at the laboratory level.
• The execution of coreflooding tests before field application, considering all
scenarios from drilling to complete the well, for the test to be representative, it is
recommended to include all the fluids involved in the testing protocol. In the process,
brines, cement, and breaker with their respective soaking times.
7.3. Partial conclusions
The optimal concentration of NP1 and the tuning with the carrier fluid were achieved
through experimental tests. Filtration volume and filter cake thickness reductions were
achieved. Carrier fluids with high NP1 concentration and surfactant content can destabilize
the colloidal suspension stability and alter the WBM properties. Before the field application,
no significant effects were evidenced in reducing the radius of invasion using the WBM with
NP1. A further evaluation is required sensitizing the concentration of the additive of the
WBM and considering possible contaminants. The PI values could not be compared
between wells A and B since a high draw-down performed in well B generated fines
migration, causing severe formation damage.
7.4. References
[1] A. S. Borisov, M. Husein, and G. Hareland, "A field application of nanoparticle-based invert emulsion drilling fluids," Journal of Nanoparticle Research, vol. 17, pp. 1-13, 2015.
[2] L. Torrado, L. C. Carvajal-Arenas, P. Mann, and J. Bhattacharya, "Integrated seismic and well-log analysis for the exploration of stratigraphic traps in the Carbonera Formation, Llanos foreland basin of Colombia," Journal of South American Earth Sciences, vol. 104, p. 102607, 2020.
[3] L. J. Giraldo, M. A. Giraldo, S. Llanos, G. Maya, R. D. Zabala, N. N. Nassar, et al., "The effects of SiO2 nanoparticles on the thermal stability and rheological behavior of hydrolyzed polyacrylamide based polymeric solutions," Journal of Petroleum Science and Engineering, vol. 159, pp. 841-852, 2017.
Chapter 7 165
8. Conclusions and recommendations
8.1. Conclusions
This study provides experimental results and phenomenological insights of colloidal
suspension stability (drilling fluids) and its influence in the filtration process in the presence
of SiO2 NPs. The evaluation includes the particle size, charge, and concentration variations
of the SiO2 NPs in the polymer-CaCO3-rock. The key factor in the colloidal stabilization
mechanism hypothesis is the NPs with the smallest size, highest total acidity, and the most
negative value of zeta potential had the highest capacities of filtration volume and filter cake
thickness reduction. These factors provide the repulsion forces between NPs and solid
particles, improving the rheological and filtration properties. The adsorption of polymer onto
SiO2 NPs (attractive forces) strengthen the viscoelastic structure and reduce the
degradation of WBM viscosity under thermal degradation.
Moreover, xanthan gum interaction with CaCO3 strengthened the filter cake as the polymer
fills up the void among CaCO3 particles. Xanthan gum attachment to the CaCO3 particles
arises from the electrostatic interactions between the anionic polymer groups and the
hydrated calcium sites on the CaCO3 surface. Once the filter cake has formed, the distance
between particles is significantly reduced, favoring particles attractive forces. SiO2 NPs
modify the morphological structure and thickness of the filter cake through physical and
electrochemical interactions. Large particles are deposited in the bottom of the filter cake.
As the filtrate flow decreases, smaller particles are deposited on the top surface. Also, the
roughness surface filter cake was reduced. SiO2 NPs presented a physical mechanism
occupying the empty spaces in the porous media and retained in the porous surface due to
the affinity between the silica groups of the rock and the active sites of the SiO2 NPs. Hence,
the SiO2 NPs could interact in the following order with each item evaluated: Polymer <
CaCO3 < rock. In the polymer case, they interact stronger with the rock, CaCO3, and
polymer solution in that order. Otherwise, once the SiO2 NPs enter the formation through
the mud filtering, they are retained in the porous medium and cover the surface. This
Chapter 8 167
mechanism allows NPs to alter the properties of the rock. Likewise, these can be located
between the fluids (water/oil) interface and reduce the tension between the fluids. Finally,
the concepts were used to design a nanofluid to be applied in a field application drilling
fluid. Strategies and methodologies for application and scaling the WBM with NPs in the
drilling were proposed.
8.2. Recommendations
According to the results obtained, the following recommendations are proposed:
• To explore other NPs such as CaCO3, Fe2O3, Al2O3, etc.
• To synthesize and evaluate nanocapsules with surfactants and the content could
be released inside the rock.
• To evaluate the effect of CaCO3 and polymer concentration.
• To include salt content or contamination factors that are presented during the drilling
process.
• To corroborate the thermal stability of drilling fluids using NPs with different chemical
nature and other polymers.
• To evaluate the effect of SiO2 NPs in oil-based drilling fluids.
• To evaluate the effect of SiO2 NPs in polymer-based drilling fluids without the
presence of CaCO3.
• To evaluate the effect of SiO2 NPs in the inhibition of the formation damage after
completion of fluids injection.
• To evaluate the effect of surfactants-based drilling fluids.
• Expand the rheological evaluation of drilling fluids considering the concept of
viscoelastic polymers.
• To evaluate the presence of other starch, polyanionic cellulose and starches.
9. Publications and awards
As scientific contribution of this Ph.D. thesis, the following documents have been published:
9.1. Scientific papers and book chapter
• Influence of size and surface acidity of silica nanoparticles on inhibition of the
formation damage by bentonite-free water-based drilling fluids. Part I: nanofluid
design based on fluid-nanoparticle interaction. Advances in Natural Sciences:
Nanoscience and Nanotechnology 10, no. 4 (2019): 045020.
• Influence of size and surface acidity of silica nanoparticles on inhibition of the
formation damage by bentonite-free water-based drilling fluids. Part II: dynamic
filtration. Advances in Natural Sciences: Nanoscience and Nanotechnology 11,
no. 1 (2020): 015011.
• Effect of Silica Nanoparticles on Thermal Stability in Bentonite Free Water-Based
Drilling Fluids to Improve its Rheological and Filtration Properties After Aging
Process. In Offshore Technology Conference Brazil. Offshore Technology
Conference, 2019.
• A Theoretical and Experimental Approach for Understanding the Interactions
Among SiO2 Nanoparticles, CaCO3, and Xanthan Gum Components of Water-
Based Muds. Fuel & Energy, 2021.
• Book Chapter (In review): Nanotechnology for Enhancing In-Situ Recovery and
Upgrading of Oil and Gas Processing. Chapter 6, Design of a Novel Double Purpose
Drilling Fluids Based on the Nanotechnology: Drilling-Induced Formation Damage
Reduction and Improvement of the Mud Filtrate Quality.
• In review: Effect of SiO2 Nanoparticles on External Filter Cake Morphology of Water-
Based Mud: Study of its Build Up Mechanism through SEM and AFM Image
Processing. Journal of Petroleum Science and Engineering, 2020.
Publications and awards 172
9.2. Oral presentations
• Design of a Novel Double Purpose Drilling Fluids Based on the Nanotechnology:
Drilling-Induced Formation Damage Reduction and Improvement of the Mud Filtrate
Quality. 2020 Latin America and the Caribbean Virtual Regional Student Paper
Contest, May 2020.
• Efecto de las nanopartículas de sílice en la estabilidad térmica de los fluidos de
perforación base agua libres de bentonita para el mejoramiento de las propiedades
reológicas y de filtración después de los procesos de añejamiento. XVIII Congreso
Colombiano de Petróleo y Gas, Bogotá, Colombia, November 2019.
• Effect of Silica Nanoparticles on Thermal Stability in Bentonite Free Water-Based
Drilling Fluids to Improve its Rheological and Filtration Properties After Aging
Process. Offshore Technology Conference Brazil (OTC Brazil 2019), Río de
Janeiro, Brazil, October 2019.
• Effect of Silica Nanoparticles on Thermal Stability in Bentonite-Free Water-Based
Drilling Fluids to Improve its Rheological and Filtration Properties Subsequent to the
Aging Process. IEA Technology collaboration program on EOR, Cartagena de
Indias, Colombia, September 2019.
• Study of the Nanoparticle/Polymer /CaCO3 interactions to optimize the stability of
the colloidal suspension and the packing of the solids. 2° Congreso
Latinoamericano de Ingeniería – Retos en la formación de Ingenieros en la era
digital, Cartagena de Indias, Colombia, September 2019.
• Influence of size and surface acidity of silica nanoparticles on inhibition of the
formation damage by bentonite-free water-based drilling fluids. VII Escuela de
Verano: Nuevas tecnologías en productividad y recobro mejorado de gas y aceite,
Universidad Nacional de Colombia, Medellín, Colombia, August 2019.
• Influence of size and surface acidity of silica nanoparticles on inhibition of the
formation damage by bentonite-free water-based drilling fluids. 2019 South America
and Caribbean Regional Student Paper Contest, Santa Cruz de la Sierra, Bolivia,
May 2019.
• Influence of size and surface acidity of silica nanoparticles on inhibition of the
formation damage by bentonite-free water-based drilling fluids. SPE Colombia
National Student Paper Contest, Bucaramanga, Colombia, April 2019.
Publications and awards 173
• Influence of size and surface acidity of silica nanoparticles on inhibition of the
formation damage by bentonite-free water-based drilling fluids. SPE Technical
Conference 2018 (SPETC 2018), Medellín, Colombia, August 2018.
9.3. Awards
• ACIPET price to innovation: Influence of size and surface acidity of silica
nanoparticles on inhibition of the formation damage by bentonite-free water-based
drilling fluids. 2018.
• Finalist, Latin America and the Caribbean Virtual Regional Student Paper Contest.
2019 and 2020.