experimental study of rheological properties of aphron based drilling...

Scientia Iranica C (2017) 24(3), 1241{1252

Sharif University of TechnologyScientia Iranica

Transactions C: Chemistry and Chemical Engineeringwww.scientiairanica.com

Experimental study of rheological properties of aphronbased drilling uids and their e�ects on formationdamage

M. Heidaria, Kh. Shahbazia;� and M. Fattahib

a. Department of Petroleum Engineering, Ahwaz Faculty of Petroleum Engineering, Petroleum University of Technology, Abadan,Iran.

b. Department of Chemical Engineering, Abadan Faculty of Petroleum Engineering, Petroleum University of Technology, Abadan,Iran.

Received 16 September 2015; received in revised form 31 December 2016; accepted 4 March 2017

KEYWORDSDrilling uid;Polymer-surfactant;CGA;Rheologicalproperties;Bubble sizemeasurement.

Abstract. Drilling uid is one of the most important and expensive aspects of any drillingprocess. Colloidal Gas Aphron (CGA) has been found e�ective in controlling the �ltrationrate by bridging the pores of the reservoir rock; hence, reducing the formation damage.This work aims to synthesize the CGA in water based drilling uids to study the stability,rheology, �ltration loss characteristics and formation damage properties of the resulting uid. Besides, an investigation on type of polymer, surfactant, and their concentratione�ects on the characteristics of the uid, as well as optimum ratios of polymers in drilling uid was performed. Experimental results showed that Xanthan Gum (XG) providesmore acceptable rheological properties (especially viscosity) in comparison to Guar Gum(GG) for preparing the base uid. Moreover, the Sodium Dodecyl Sulfate (SDS) producesmore stable micro-bubbles than Hexadecyl Trimethyl Ammonium Bromide (HTAB) as asurfactant. Bubble size measurement to observe the e�ect of polymer, surfactant typeand concentration was performed. Through the experiments, the pH of the drilling uidwas monitored which proved the CGA introduced the best performance around a pH of 9.Furthermore, a XG/GG ratio of 3:1 is suggested to reduce the cost while maintaining the uid properties.© 2017 Sharif University of Technology. All rights reserved.

1. Introduction

When a well is drilled, the pressure in the wellboreis usually kept above the pressure in the formationto prevent formation uids entering the well. Thisis called overbalanced drilling (OBD) and has severallimitations. It can cause formation damage whenthe drilling mud is forced into the formation ( uidinvasion). Large amounts of the drilling mud can be

*. Corresponding author.E-mail addresses: [email protected] (M.Heidari); [email protected] (Kh. Shahbazi);[email protected] (M. Fattahi)

uncontrollably lost into the formation (lost circulation).Di�erential sticking is also a problem associated withOBD. Underbalanced drilling (UBD) as an alternativeto OBD can overcome these issues while UBD, the well-bore pressure, is maintained lower than the formationpressure. The primary advantage of UBD is preventing uid invasion and the resultant formation damage. Italso helps the reduction of di�erential sticking andincreasing the rate of penetration. However, UBD isan expensive task and meeting the safety requirementsis not easy. A lot of problems like borehole instability,well control, and use of special downhole equipmentcome up [1]. At-balance drilling means drilling with thewellbore uid pressure closely matching the formation

1242 M. Heidari et al./Scientia Iranica, Transactions C: Chemistry and ... 24 (2017) 1241{1252

uid pressure so that there is minimal uid invasionand the formation uids do not come into the wellbore.In an at-balance situation, use of CGA based drilling uids helps to produce lower drilling uid densities andto seal the pores by bridging [2]. Such a system can beparticularly useful in drilling depleted and low pressurereservoirs.

Aphrons are colloidal dispersions of micro-bubbleswith diameters ranging from 10 to 100 �m [3]. Anaphron is made of a core, which is often a sphericalinternal phase, encapsulated in a thin shell. In caseof a gaseous core, this structure is called CGA [3].When the internal core is a liquid, normally oil based,it is called colloidal liquid aphron [4]. Finally, theaphrons with cores formed of water-in-oil emulsion arecalled colloidal emulsion aphrons [5]. Todays, the useof CGA based uids is increasing in the petroleumindustry because these uids exhibit properties thatare desirable in operations in many �elds [1,2,6-9].The potential of aphrons as components of drilling uids is due to their ability to form a solid, free,tough, and elastic internal bridge in pore networks orfractures to minimize deep invasion through air micro-bubbles [10,11]. Moreover, the high carrying capacity,minimum amount of uid placed in the formation, andgood uid recovery after treatment are some of theadvantages that CGA based uids utilized during theoperations [2,12,13].

CGAs incorporated into drilling mud to forma CGA drilling uid have been studied extensively,too. Brookey [2] suggested the use of CGA drill-in uid while drilling at balance. Growcock [14] madea detailed investigation into increasing wellbore sta-bilization and reservoir productivity by using aphrondrilling uid technology. Aphron based drilling uidsare non-coalescing and can be re-circulated [2] withoutbeing a�ected by downhole equipment. Downhole toolssuch as MWD, turbines, and motors do not su�erinterference by aphrons [15].

CGAs can be produced easily on the surface andno separate equipment like compressors are requiredto inject gases at high pressure. In UBD, the pres-ence of air creates a condition of extreme corrosionwhere air and water are in constant contact with thedrill string [2]. Corrosion problems are reduced withaphronized uids due to the fact that most of theair is encapsulated in the aphron shell. Besides, it iscommon to add an oxygen scavenger to the drilling uidformulation [14]. Thus, after the aphrons are created,the oxygen is scavenged by one of the components inthe uid, leaving the aphrons with a core of nitro-gen [14]. This gives aphrons the non-corrosive nature.Subsequently, the usefulness of aphrons for di�erenttypes of applications has been suggested.

For stability of the CGA, the concentration of thesurfactant should be greater than the Critical Micelle

Concentration (CMC) [16,17], which varies for eachtype of surfactant. When a concentration of less thanthe CMC is used, the CGAs will be large in size [17].CMC measuring could be achieved through surfacetension measurements. At the CMC and beyond, thesurface tension will no longer change with concentra-tion. The CMC for some of the surfactants utilizedto build CGAs has been reported in the literature.For example, the CMC of HTAB in water is approx-imately 350 ppm and for sodium dodecyl benzenesulfonate is about 500 ppm [16]. The surface activityand aggregation behavior of the surfactant a�ect thestability and other physico-chemical properties of thegenerated micro bubbles in CGA. Therefore, selectionof a suitable surfactant is important for the generationof micro bubbles with the desired rheological and�ltration properties [18].

The purpose of a surfactant is to be adsorbed atthe interface, thereby reducing surface tension. Theutilization of tergitol and lauryl alcohol as surfactantsfor CGA generation was investigated by Sebba [3].Amiri and Woodburn [19] used a cationic TetradecylTrimethyl Ammonium Bromide (TTAB) surfactant foraphron generation. Roy et al. [16] tested an anionicsurfactant Sodium Dodecyl Benzene Sulfonate (SDBS)and a cationic surfactant of HTAB. Save et al. [20] used4 cationic surfactants: Dodecyl Trimethyl AmmoniumChloride (DTAC), Cetyl Trimethyl Ammonium Chlo-ride (CTAC), Cetyl Pyridinium Chloride (CPC), anddimethyl distearyl ammonium chloride (DMDSAC).Save et al. [20] also tested anionic SDBS and SodiumLauryl Sulfate (SLS). Chaphalkar [21] used tergitol15-S-12 as a non-ionic surfactant, SDBS as the an-ionic surfactant, and HTAB as the cationic surfactant.Hashim et al. [22,23] utilized the dilute SDS and BenzylDimethyl Hexadecyl Ammonium chloride (BDHA) foraphron generation. Bjorndalen and Kuru [24] usedSDBS and HTAB as surfactants for their study onCGAs. Dai and Deng [25] tried hexadecyltrimethylammonium chloride (HTAC) as the surfactant. Thegeneration of aphrons in oil and its detailed formulationwere investigated by Growcock et al. [11]. However,they did not give any speci�c information as to whattype/class of surfactant was used.

Xanthan Gum (XG) polymer, a high-molecular-weight natural polysaccharide, is a common drilling uid additive for controlling uid loss and viscosityimprovement in the formulation of both oil-based andwater-based drilling muds [26,27]. It hydrates rapidlyin cold water without lumping to give a reliable viscos-ity and use it as a thickener, stabilizer, emulsi�er, andfoaming agent [28]. It has tolerance to changes of tem-perature, acidity, and alkalinity. From the viewpoint ofenvironmental concerns, XG presents good propertiesfor drilling mud applications [29]. Furthermore, acritical concentration of 1.25 to 1.5 lb/bbl must be

M. Heidari et al./Scientia Iranica, Transactions C: Chemistry and ... 24 (2017) 1241{1252 1243

present in the formulation of a drilling uid to provideadequate cutting transport capacity [26]. Bjorndalenand Kuru [24] prepared aphron uids with a water-XGmixture as a base uid. They used the XG biopolymeras a viscosi�er and aphron stabilizer. Spinelli etal. [30] prepared the base uids for aphronization bymixing the organic phase at di�erent concentrations oforganophilic clay and viscosi�ers.

From laboratory and �eld tests it has been foundthat the combination of two major factors, i.e. drilling uid and rheology, has greater e�ect on the rate ofpenetration than any other controllable variables inthe drilling process [31]. In spite of the documentedliterature on the physicochemical characteristics andrheological behavior of CGA based drilling uids [32-43], the interpretation of the rheological model ofCGA based drilling uids has not been fully addressed.Amiri and Woodburn [19] found the average size ofthe micro bubbles to be 35 �m by analyzing throughoptical microscope. Feng et al. [44] took microscopicphotographs of the bubbles. The pictures were ana-lyzed using an image analysis tool pack to obtain thebubble size distribution. About 100-300 bubbles werecounted for each sample. Zhao et al. [45] measured 130to 240 individual bubbles using image analysis softwareand a microscope. Spinelli et al. [30] used a similarmicroscope and image analysis software combinationto work on the size distribution.

Brookey [2] presented four case studies, whereaphron uids were applied successfully. The �rstapplication was in West Texas, where a horizontal re-entry well was drilled. In the second application, ina dolomitic zone in North Texas where severe lostcirculation due to large openings existed, the use ofaphron uids made it possible to drill with no losses.In the third application, in a shale formation, the HighYield Stress Shear Thinning (HYSST) nature of theaphron uids made it possible to control invasion whileproviding borehole stability. In the fourth and lastapplications, in a sisquoc sand well (unconsolidatedpermeable sand) aphron HYSST, drilling uid providedinvasion control and avoided instability that mightbe encountered in sand wells. MacPhail et al. [46]described several case studies of wells in Alberta andMississippi. Aphron uid technology was successfullyapplied in several completion and workover applica-tions leading to reduced uid loss. Rea et al. [8] usedaphron uids as a workover uid in the Tajin �eld inEastern Mexico that the bridging provided by aphrons,leading to e�ective sealing.

The aim of this study was to investigate aphronbased drilling uid's unique characteristics and physic-ochemical properties. Rheological behavior and stabil-ity of the prepared aphronized drilling uids were alsostudied. API �ltration loss, which is a key indication inevaluating the performance of aphronized uids in pre-

venting �ltrate from entering into the formation rockand consequently minimizing formation damage, wasinvestigated. E�ects of polymer, surfactant type, andconcentration were also monitored. Furthermore, themain objective was to achieve proper formulation andoptimization of CGA characteristics and properties.The ability of the surfactant in the reduction of densityand polymer performance in enhancing the toughnessof aphrons, and the e�ect of pH on CGA characteristicsand performance with regard to its in uence on poly-mer based mud were studied. Moreover, the rheologicalcharacteristics and properties of a system containingstable micro bubbles and the bubble size distributionof aphronized uid were investigated in this research.

2. Experimental

2.1. Materials and methodsTo produce aphron in aqueous medium, distilled waterwas utilized as the base liquid for aphron. The CGA uid in this study was composed of two main materials:polymer and surfactant. The utilized polymers in thisstudy were XG and GG supplied by MI SWACO &SCOMI Oil Tools, respectively. According to the lit-erature, XG is the most e�ective viscosi�er for aphronbased uid; however, the e�ect and performance of GGwere investigated in this research.

Cationic and anionic surfactants were used toproduce the CGA. Two types of surfactants werechosen for the production of the CGA: HTAB as acationic surfactant and SDS as an anionic surfactant.These surfactants were chosen based upon the previousresearch [16,47]. In this work, we focused on the anionicsurfactant, i.e. SDS. SDS or SLS with the formulaC12H25SO4Na is an anionic surfactant made up of anorganosulfate consisting of a 12-carbon tail attached toa sulfate group. A mud mixer was used to mix thedrilling uid components. All mixing was performedby a Hamilton Beach mixer. The density of the uidwas measured using either a mud balance or, in the casewhere the density was low, a digital scale and �xed uidvolume was used. To determine acidity or alkalinityof solutions, a pH/mV meter automatic temperaturecompensation AZ brand, model 8601, was used. Tocontrol and compensate the pH of the solution in range,caustic soda and citric acid were added to increase anddecrease the pH, respectively.

During all steps, an OFITE VG meter, Fannmodel 35A, to obtain rheological properties was uti-lized. This type of VG meter acted as a heater,so temperature was under control according to wellconditions; also, continuous monitoring was possible bythe thermometer, which was attached to the main cap.The rotational viscometer was developed for quantita-tive and more accurate readings of the viscosity. Thedimensions of bob and rotor were chosen such that the


dial reading on the viscometer was equivalent to theapparent viscosity in centipoises at a rotor speed of300 rpm. The apparent viscosities were calculated as:

�a =300�NN

; (1)

where, �N is the dial reading in degrees, and N is therotor speed in rpm. The apparent viscosity, plasticviscosity, and yield point were calculated from 300 and600 rpm readings using the following formulae from theAPI recommended practice of standard procedure for�eld testing drilling uids:

�p = �600 � �300; (2)

�y = �300 � �p; (3)

where, �p is the plastic viscosity in centipoises, and�600 and �300 are the dial readings at 600 rpm and300 rpm, respectively. �y is the yield point in Ibf=100sq ft. Based on the rheology theory of power law uid,the consistency coe�cient and the behavior index ofdrilling uid were calculated from 300 and 600 rpmreadings using the following formulae:

K =0:51 �300

511n: (4)

For behavior index:

n = 3:322 log��600

�300

�; (5)

where K is the consistency index in dyne.sn /cm2

and n is the ow behavior index. Standard API�ltration tests were done using a standard API �lterpress to determine �ltration volume as a key indicatorto determine the amount of uid invasion towardformation and its related formation damage. Theequipment was supplied by OFITE testing equipmentInc. (MI SWACO mud lab. on a Jack Up Rig). Thestandard API �lter press had an area of 45 cm2 andthe tests were operated at a pressure of 100 psig androom temperature of about 75�F. The �ltrate volumecollected in a period of 30 min was reported as standardwater loss.

In this study, the micro bubble samples wereimaged immediately following the aphron generationprocess by using a Sony ExwaveHAD digital videocamera attached to a SaIran IMM-420 microscope witha high degree of magni�cation. The aim was to observethe e�ect of biopolymer and surfactant type as well asconcentration and sizes of micro bubbles.

2.2. Preparation of aphronized based uidPolymers including XG (from 0 to 2 lb/bbl) and GG

(from 0 to 2 lb/bbl) were added to water in order toprepare the base uid. The base uid was generatedby smoothly mixing the appropriate amount of polymerwith 350 mL of distilled water for production of aphron.To monitor and control the e�ect of pH (at 5, 9,and 12), additives (i.e., caustic soda and citric acid)were added to the base water in order to convertthe media to an alkaline or acidic environment. Thesolutions were agitated for 20 min, starting with a lowspeed of 3000 rpm and gradually increasing the speedto a maximum of 8000 rpm, to avoid formation oflocal viscosi�ed agglomerates, which are known as \�sheyes". Moreover, a micro bubble suspension was easilygenerated using a spinning disc type generator witha surfactant solution [48]. During preparation of thebase uid, the temperature of the mixture may increasedue to mixing which may cause instability in the microbubbles, so it is recommended to wait around 5 minfor the mixture to adapt to room temperature. Next,the surfactants including SDS (0.5 and 0.75 lb/bbl)and HTAB (0.5 and 0.75 lb/bbl) were gently mixedat 3000 rpm; then, the speed increased to 8000 rpmwithin 2 min. The stability and rheological propertiesof CGA were in uenced not only by the average size ofthe bubbles but also by the bubbles size distribution.Microscope-assisted photographic techniques are themost common methods for bubble size determination.Time is crucial in this technique because, under staticconditions, the size and shape of the bubbles changedue to di�usion problems. To minimize these problems,the micro bubble samples were imaged immediatelyfollowing the aphron generation process. Aphronizeddrilling uids are compressible non-Newtonian uidsand behave like yield pseudo-plastic type uids withshear thinning characteristics [40].

3. Results and discussion

Rheology, bubble size distribution, density, and �ltra-tion loss of aphronized uids were investigated usingdi�erent types of polymers and surfactants.

3.1. E�ect of rheologyRheological properties of aphronized uids generatedfrom two types of anionic and cationic surfactantsare summarized in Table 1. Compared to the base uid, both SDS and HTAB were able to improveplastic viscosity and yield point. Results indicatedthat by increasing surfactant concentration, rheologicalproperties improved for both surfactants, while SDSdemonstrated better performance. This means SDSgenerates more micro-bubbles due to better rheologicalproperties. In other words, by adding the same amountof surfactants (i.e., 0.5 and 0.75 lb/bbl to 2 lb/bblof XG solution), the aphronized uid prepared bySDS reveals more desirable properties than HTAB.


Table 1. E�ect of surfactant type and concentration on rheological properties of CGA uid prepared by 2 lb/bbl XGsolution.

Fluid Surfactantconcentration

AV PV YP GS(10 sec/10 min)

Base uid 0 23.5 10 27 14/16Base uid + SDS 0.5 58 26 64 22/30

0.75 64.5 28 73 23/32Base uid + HTAB 0.5 30.5 16 29 16/18

0.75 34 17 33 17/19

Furthermore, the data proved that by increasing sur-factant concentration, the yield point increased drasti-cally (especially for SDS, which increased from 64 for0.5 lb/bbl to 73 for 0.75 lb/bbl) while plastic viscosityremained nearly constant (16 at 0.5 lb/bbl and 17for 0.75 lb/bbl for HTAB PV). Both surfactants wereable to increase the gel strength of the base uid,but di�erent concentrations of the surfactant had littlee�ect on gel strength. Overall, adding a surfactant im-proved the rheological properties of aphron based uidsand increasing surfactant concentration improved theseproperties due to the generation of more stable bubbles.

In order to observe the pH e�ect on CGA rheol-ogy, citric acid and caustic soda were added to the basewater to produce an acidic and alkaline environment.Aphronized uid was prepared with a 2 lb/bbl XG and0.75 lb/bbl SDS solution. The results of pH e�ects onrheology are illustrated in Table 2.

By adding the proper amount of citric acid orcaustic soda, pH of the solution was controlled around 5and 12, respectively, while the pH of the base uid was7 due to the distilled water, which was used to make thesolution. The data in Table 2 shows that plastic viscos-ity decreases slightly in an acidic or basic environment,but the environment has no signi�cant e�ect on yield

Table 2. E�ect of pH on rheological properties of CGA uid prepared by 2 lb/bbl XG and 0.75 lb/bbl SDSsolution.

pH AV PV YP GS(10sec/10min)

5 60.5 24 73 22/339 67 30 74 24/3412 62 25 74 21/32

point. In other words, plastic viscosity shows the mostchanges with regard to di�erent media. Moreover, gelstrength remained nearly constant for the di�erent pH.It was observed that better rheological performanceoccurred when the pH of the base uid was around9. Overall, the pH value had no very signi�cant e�ecton the mean size, stability, and rheological propertiesof bubbles. In the pH ranges over 7, the SDS surfactantin the solution was present mainly in the anionicform, which was con�rmed by the open literature [49].The electrostatic interactions of the ionic form of thesurfactant contributed to the stability of CGA, whichwas consistent with observations reported by Jauregi etal. [50]. The results showed that the viscosity of CGAsolution was low as it had uidity and could be easilyseparated from the bulk liquid phase.

E�ect of polymer type and concentration onrheological properties of aphronized uids prepared by0.75 lb/bbl SDS is summarized in Table 3. Previous re-search e�orts [51] have been focused on the acceptablerheological properties of XG; however, the practical useof XG is limited due to its high cost. Therefore, to givethe desired rheological properties, GG was added in dif-ferent proportions as an alternative to reduce the cost.

Based on Table 3, the performance of XG wasbetter than that of GG, as was expected.

To draw shear stress versus shear rate, there aresome relationships due to bob and rotor dimensions(i.e., radius and length), which are as follows:

� =360:5�2�hr2 ; (6)

=5:066Nr2 ; (7)

Table 3. E�ect of polymer type and concentration on rheological properties of CGA prepared by 0.75 lb/bbl SDS.

AdditivesAV PV YP GS

(10 sec/10 min)XG(lb/bbl)

GG(lb/bbl)

2.0 0.0 64 28 73 23/331.5 0.5 63 27 72 21/301.0 1.0 57.5 23 69 19/230.5 1.5 53.5 21 65 17/200.0 2.0 45 21 48 14/18


where, r = 1:7245 and h = 3:8 for Fann 35A.The shear stress versus shear rate was presented

in Figure 1(a) to (c) based upon the reading data of�. The addition of GG to XG reduced the quality ofthe aphronized uid. However, as Figure 1(c) presents,when they were mixed in a ratio of 3 to 1, the rheologydid not change signi�cantly. This could reduce the �nalcost of drilling uid while maintaining the quality atthe same level.

3.2. E�ect of bubble size distributionAverage bubble diameter and size distribution ofaphrons are very important factors, which a�ect the

Figure 1. E�ect of (a) surfactant type and concentration,(b) pH, and (c) polymer type and concentration onrheological properties of the prepared CGA uid.

pore bridging and blockage mechanism. Bubble sizedistribution is one of the indicators that re ect thequality of the generated aphron. Immediately afterpreparation of the CGA uid, a small sample of uidwas taken for imaging and size measurements. In theseexperiments, the base water pH was set at 9, wherethe best rheology performance was obtained. Figure 2shows two microscopic pictures taken from aphronized uids prepared by SDS and HTAB surfactants (with0.75 lb/bbl concentration) while the base uid wascomposed of water and 2.0 lb/bbl XG as the polymer.\Golden Ratio" software (Version 3.1.2) was used tomeasure the size of the bubbles. In order to measurethe bubble size, a line with a speci�ed length was givento the software. The lengths as well as the angle andthe ratio of the two lines were displayed.

Table 4 illustrates the e�ect of surfactant typeand concentration, polymer concentration, and pH onthe average bubble size of CGA uids. Results showthat by increasing the surfactant concentration, the

Figure 2. Microscopic picture of aphron micro bubblesfrom (a) 0.75 lb/bbl SDS and (b) 0.75 lb/bbl HTABsolutions at concentration of 2 lb/bbl XG.


Table 4. E�ect of surfactant type and concentration, polymer concentration, and pH on average bubble size.

AdditivespH Average bubble

size (�m)Surfactanttype

Surfactantconcentration

(lb/bbl)

Polymerconcentration

(lb/bbl)SDS 0.5 2 9 79SDS 0.75 2 9 77SDS 1 2 9 65SDS 0.5 1.5 9 84SDS 0.5 2.5 9 67SDS 0.75 2 5 81SDS 0.75 2 12 80

HTAB 0.75 2 9 84

average bubble size decreases. One reason could be theavailability of more surfactant molecules to generateviscous shells, which resulted in the generation of moremicro bubbles and a reduction in average bubble sizes.On the other hand, by increasing the polymer concen-tration, the average bubble size decreased. Increasingpolymer concentration caused the base uid viscosityto increase and reduced the shear stress exerted on the uid by the spinner. Therefore, the size of aphronswas reduced. Table 4 shows that acidic or alkalineenvironments led to higher average bubble sizes, whichcould be a result of lower viscosity in those conditions(Table 4). Nonetheless, as Table 4 re ects, CGA uidgenerated from HTAB had higher average bubble sizesthan the one prepared by SDS.

The e�ect of polymer concentration on bubblesize distribution can be seen in Figure 3, which showsthe average bubble size in the aphron based uid withXG as the polymer in concentrations of 1.5, 2.0, and2.5 lb/bbl and SDS as the surfactant with concen-tration of 0.5 lb/bbl. Comparing Figure 3(a) and(c), it is clear that by increasing polymer concentra-tion, the fraction of small-diameter bubbles increasessigni�cantly. In other words, if we increase polymerconcentration from 1.5 to 2.5 lb/bbl, the peak of sizedistribution graph will shift from 60-80 to 40-60 �m,which results in lower average bubble sizes.

The fraction of bubbles with small diameters en-hanced as the surfactant concentration was increased.This fact was obtained at 2.0 lb/bbl of XG as thepolymer while the pH was controlled around 9 and theconcentration of SDS as the surfactant was increasedfrom 0.5 lb/bbl to 1.0 lb/bbl, gradually. Moreover,the e�ect of surfactant type is presented in Figure 4,with the same concentrations of polymer (2.0 lb/bbl)and surfactant (0.75 lb/bbl). Besides, SDS is ableto produce smaller micro bubbles than HTAB. Thisshows that SDS performed better in generating theaphronized uids.

The e�ect of base water pH on size distribution ofaphron bubbles indicated that in acidic and extremelybasic environments, a wide range of micro bubbles wereformed in comparison with the situation where pH waskept around 9. In other words, when pH uctuatedaround 9, average bubble sizes varied both up and downand their distribution was a�ected, which led to lowerquality.

3.3. E�ect of densityThe density of CGA uid shows the quantity of microbubbles and the potential of the surfactant to formaphrons. The e�ect of surfactant concentration ondensity has been studied in several investigations [52].It has been shown that increasing surfactant concen-tration might reduce the density of aphronized uiddue to the increase in the number of micro bubblesformed. The e�ect of polymer concentration has alsobeen investigated in the previous research, which showsthat higher polymer concentrations result in higherdensities.

The e�ects of two di�erent types of surfactants(an anionic (SDS) and a cationic (HTAB) surfactant)and their concentrations on the density of aphronized uid are indicated in Figure 5. As it is shown, addingsurfactant reduces solution density that is obviousdue to the formation of micro bubbles. It might beconcluded from Figure 5 that SDS reduces the densityof CGA more than HTAB does. This indicates thatSDS is able to generate more micro bubbles than HTABdoes at the same concentration. SDS at 0.75 lb/bbl ofconcentration reduced the density of 2 lb/bbl XG base uid from 61 to 25 pcf, whereas HTAB, at the sameconcentration, reduced the density to 34 pcf.

The e�ect of polymer type on the density ofCGA uid is shown in Figure 6. This �gure indicatesthat the CGA prepared with XG base uid providedlow density compared to CGA derived from GG. Thisobservation recon�rms the above-mentioned rheology


Figure 3. Bubble size distribution of the prepared CGA uid by (a) 1.5 lb/bbl XG, (b) 2.0 lb/bbl XG, and (c)2.5 lb/bbl XG and 0.5 lb/bbl SDS.

results, where XG provided better rheological proper-ties than GG did. Therefore, CGA uid derived fromXG is able to generate more stable micro bubbles andreduces density of the solution. It should be pointedout that the density measurements were taken underatmospheric pressure conditions. As pressure increases(e.g., in downhole conditions), the aphrons will becompressed and the density of uid increases.

3.4. Filtration control e�ectFiltration loss control is one of the most important

Figure 4. Bubble size distribution of the prepared CGA uid by 2 lb/bbl XG and di�erent surfactants of (a)0.75 lb/bbl SDS and (b) 0.75 lb/bbl HTAB.

Figure 5. The e�ect of surfactant type and concentrationon the density of CGAs for 2 lb/bbl solution of XG base uid.

aspects of any drilling uid. The viscosity, quan-tity, and size of aphronized uid can a�ect theamount of �ltration loss. Previous studies haverevealed that by increasing surfactant and polymerconcentrations, the �ltration loss is reduced in CGA uids. Increasing surfactant concentration will in-crease the amount of micro bubbles, which act likea solid free bridging material and reduce �ltrationloss. On the other hand, by increasing polymer con-


Figure 6. E�ect of polymer type on CGA density at 0.75lb/bbl SDS and 2 lb/bbl polymer concentrations.

centration, the viscosity of aphronized uid increases,which has a direct e�ect on reduction of �ltrationloss.

The e�ect of surfactant type on �ltration loss isillustrated in Figure 7, where the CGAs are preparedwith 2 lb/bbl solution of XG base uid. CGA uidsprepared by both surfactants were able to reduce theamount of �ltration loss compared to the base uid.Moreover, as was expected, the CGA uid prepared bySDS had a better performance in controlling �ltrationloss, which is in complete agreement with results ofrheology and density. Because SDS is able to producehigher viscosity and lower density (i.e., higher numberof aphrons), it has better control on �ltration loss.

E�ect of polymer type and concentration on �ltra-tion loss of aphronized uids is illustrated in Figure 8.Filtration loss increased from 19 mL/30 min for CGA uid prepared by 2.0 lb/bbl XG to 33 lb/bbl for 2.0lb/bbl GG, which shows that XG is greatly superiorto GG in the case of �ltration control. In addition,�ltration loss of CGA uid prepared by 1.5 lb/bblXG and 0.5 lb/bbl GG was nearly same as that ofCGA uid prepared by 2.0 lb/bbl XG (Figure 8).In the 5 CGA-based uids prepared by formulatingdi�erent concentrations of XG and GG, the e�ect ofaphron micro bubbles in the uid based on �ltrationloss was found to be signi�cant. In all samples, afteraphronization, �ltration loss reduction in XG was morethan that in GG. This is due to the rapid ow of themicro bubbles relative to the base uid (i.e., bubbly ow) and also the capability of XG aphrons to create anexternal bridge by their accumulation [51]. IncreasingXG concentration also reduces the amount of �ltrationloss in comparison to the GG, but an acceptableviscosity for controlling uid loss is essential. Besides,the shear viscosity is too high for pumps and handlingof the operations.

4. Conclusions

In this study, di�erent formulations of aphron-based

Figure 7. E�ect of surfactant type on API �ltration loss.

Figure 8. E�ect of polymer type and concentration on�ltration loss of the prepared CGA uid by 0.75 lb/bblSDS.

drilling uids were tested. E�ect of polymer as wellas surfactant type and concentration on the mainphysicochemical properties of aphronized uids, such asdensity, rheological properties, bubble size distribution,and �ltration properties, was investigated. In order toinvestigate the �ltration behavior of di�erent samplesand rheology tests, density measurement and opticalmicroscopy to visualize the bubble sizes and quantitieswere conducted. The following conclusions can bedrawn from the experimental data:

� As the polymer concentration increased at constantsurfactant concentration (for both XG and GG),the viscosity and density of the aphronized uidincreased while the volume of �ltration loss andaverage bubble size decreased (i.e., improvement inrheological uid properties);

� As the surfactant concentration increased at con-stant polymer concentration (for both SDS andHTAB), the viscosity increased while the density,�ltration volume, and average bubble size decreaseddue to the generation of more micro bubbles;

� For the same type and concentration of surfactant(SDS or HTAB), XG shows better rheological and


�ltration properties than GG. This means that XGis a better choice to generate CGA, but the costis a crucial factor. Thus, a 3:1 ratio of XG/GG isrecommended to reduce the cost while maintainingthe properties at the same level;

� For the same type and concentration of polymer(XG or GG), the anionic surfactant (SDS) showsbetter rheological and �ltration properties than thecationic one (HTAB) to generate the CGA;

� To obtain better rheological and �ltration properties(i.e., to improve conditions of CGA uids), the pHshould be kept somewhere around 9 (i.e., moderatealkaline media).

Nomenclature

CGA Colloidal Gas AphronCMC Critical Micelle ConcentrationMWD Measurement While DrillingAPI American Petroleum Institutepcf Pound per cubic foot� Shear Stress (SS) Shear Rate (SR)�0 Yield Point (YP)n Power law indexK Consistency indexAV Apparent ViscosityPV Plastic ViscosityGS Gel Strength

References

1. Ivan, C.D., Quintana, J.L. and Blake, L.D. \Aphron-base drilling uid: Evolving technologies for lost circu-lation control", Proceedings of SPE Annual TechnicalConference and Exhibition, New Orleans, Louisiana(2001).

2. Brookey, T. \Micro-bubbles: New aphron drill-in uid technique reduces formation damage in horizontalwells", Proceedings of SPE Formation Damage ControlConference, Lafayette, Louisiana (1998).

3. Sebba, F., Foams and Biliquid Foams-Aphrons , Wiley,New York, First Edition (1987).

4. Lye, G.J. and Stuckey, D.X. \Structure and stabilityof colloidal liquid aphrons", Colloids and Surfaces A:Physicochemical and Engineering Aspects, 131, pp.119-136 (1998).

5. Deng, T., Dai, Y. and Wang, J. \A new kind ofdispersion-colloidal emulsion aphrons", Colloids andSurfaces A: Physicochemical and Engineering Aspects,266, pp. 97-105 (2005).

6. Ziaee, H., Arabloo, M., Ghazanfari, M.H. andRashtchian, D. \Herschel-Bulkley rheological param-eters of lightweight colloidal gas aphron (CGA) based uids", Chemical Engineering Research and Design,93, pp. 21-29 (2015).

7. Ramirez, F., Greaves, R. and Montilva, J. \Ex-perience using microbubbles-aphron drilling uid inmature reservoirs of Lake Maracaibo", Proceedings ofInternational Symposium and Exhibition on FormationDamage Control, Lafayette, Louisiana (2002).

8. Rea, A.B., Alvis, E.C., Paiuk, B.P., Climaco, J.M.,Vallejo, M., Leon, E. and Inojosa, J. \Applica-tion of aphrons technology in drilling depleted ma-ture �elds", Proceedings of SPE Latin American andCaribbean Petroleum Engineering Conference, Port-of-Spain, Trinidad and Tobago (2003).

9. Hashim, M.A., Mukhopadhyay, S., Gupta, B.S. andSahu, J.N. \Application of colloidal gas aphrons forpollution remediation", Journal of Chemical Technol-ogy and Biotechnology, 87(3), pp. 305-324 (2012).

10. Alizadeh, A. and Khamehchi, E. \Mathematical mod-eling of the colloidal gas aphron motion through porousmedium, including colloidal bubble generation anddestruction", Colloid and Polymer Science, 294, pp.1075-1085 (2016).

11. Growcock, F.B., Khan, A.M. and Simon, G.A. \Appli-cation of water-based and oil-based aphrons in drilling uids", Proceedings of International Symposium onOil�eld Chemistry, Houston, Texas (2003).

12. Molaei, A. and Waters, K.E. \Aphron applications -A review of recent and current research", Advances inColloid and Interface Science, 216, pp. 36-54 (2015).

13. Moshkelani, M. and Chalkesh Amiri, M. \An insightinto colloidal gas aphron drainage using electrical con-ductivity measurement", Iranian Journal of Chemistryand Chemical Engineering, 27(3), pp. 63-68 (2008).

14. Growcock, F. \Enhanced wellbore stabilization andreservoir productivity with aphron drilling uid tech-nology", Final report, DOE Award Number DE-FC26-03NT42000 (2004)

15. Oyatomari, C., Orell�an, S., Alvarez, R. and Bojani,R., Application of Drilling Fluid System Based onAir Microbubbles as an Alternative to UnderbalanceDrilling Technique in Reservoir B-6-X.10-Tia Juana,Lake Maracaibo, International Association of DrillingContractors, Madrid, Spain (2002).

16. Roy, D., Valsaraj, K.T. and Kottai, S.A. \Separationof organic dyes from wastewater by using colloidal gasaphrons", Separation Science and Technology, 27(5),pp. 573-588 (1992).

17. Longe, T.A. \Colloidal Gas Aphrons: Generation,Flow Characterization, and Application in Soil andGroundwater Decontamination", Ph.D. Thesis, Vir-ginia Polytechnic Institute and State University, Vir-ginia (1989).

18. Arabloo Nareh0ei, M., Pordel Shahri, M. and Zamani,M. \Preparation and characterization of colloidal gas


aphron based drilling uids using a plant-based sur-factant", Proceedings of SPE Saudi Arabia SectionTechnical Symposium and Exhibition (2012).

19. Amiri, M.C. and Woodburn, E.T. \Method for thecharacterisation of colloidal gas aphron dispersions",Chemical Engineering Research and Design, 68, pp.154-160 (1990) .

20. Save, S.V., Pangarkar, V.G. and Vasanth Kumar, S.\Intensi�cation of mass transfer in aqueous two-phasesystems", Biotechnology and Bioengineering, 41(1),pp. 72-78 (1993).

21. Chaphalkar, P.G. \Characterization and application ofcolloidal gas aphrons for groundwater remediation",Ph.D. Thesis, Baton Rouge, Louisiana State Univer-sity (1994).

22. Hashim, M.A., Dey, A., Hasan, S. and Sen Gupta, B.\Mass transfer correlation in otation of palm oil bycolloidal gas aphrons", Bioprocess Engineering, 21, pp.401-404 (1999).

23. Hashim, M.A., Kumar, S.V. and Sen Gupta, B.\Particle-bubble attachment in yeast otation by col-loidal gas aphrons", Bioprocess Engineering, 22, pp.333-336 (2000).

24. Bjorndalen, N. and Kuru, E. \Physico-chemical char-acterization of aphron-based drilling uids", Journalof Canadian Petroleum Technology, 47(11), pp. 15-21(2008).

25. Dai, Y. and Deng, T. \Stabilization and characteri-zation of colloidal gas aphron dispersions", Journal ofColloid and Interface Science, 261, pp. 360-365 (2003).

26. Caenn, R. and Chillingar, G.V. \Drilling uids: Stateof the art", Journal of Petroleum Science and Engi-neering, 14, pp. 221-230 (1996).

27. Navarrete, R.C., Dearing, H.L., Constien, V.G.,Marsaglia, K.N., Seheult, J.M. and Rodgers, P.E.\Experiments in uid loss and formation damage withXanthan-based uids while drilling", Proceedings ofIADC/SPE Asia Paci�c Drilling Technology, KualaLumpur, Malaysia (2000)

28. M'bodj, O., Kbir Ariguib, N., Trabelsi Ayadi, M. andMagnin, A. \Plastic and elastic properties of the sys-tems interstrati�ed clay-water-electrolyte-xanthan",Journal of Colloid and Interface Science, 273, pp. 675-684 (2004).

29. Arabloo, M., Pordel Shahri, M. and Zamani, M.\Characterization of colloidal gas aphron uids pro-duced from a new plant-based surfactant", Journal ofDispersion Science and Technology, 34(5), pp. 669-678(2013).

30. Spinelli, L.S., GNeto, G.R., Freire, L.F.A., Monteiro,V., Lomba, R., Michel, R. and Lucas, E. \Synthetic-based aphrons: Correlation between properties and�ltrate reduction performance", Colloids and SurfacesA: Physicochemical and Engineering Aspects, 353, pp.57-63 (2010).

31. Kok, M.V. \Statistical approach of two-three pa-rameters rheological models for polymer type drilling uid analysis, Energy Sources", Part A: Recovery,Utilization, and Environmental E�ects, 32, pp. 336-345 (2009).

32. Zamora, M., Je�erson, D.T. and Powell, J.W. \Hole-cleaning study of polymer-based drilling uids", Pro-ceedings of SPE Annual Technical Conference andExhibition, Houston, Texas (1993).

33. Kelessidis, V. and Maglione, R. \Modeling rheologi-cal behavior of bentonite suspensions as Casson andRobertson-Sti� uids using Newtonian and true shearrates in Couette viscometry", Powder Technology, 168pp. 134-147 (2006).

34. Kelessidis, V., Maglione, R., Tsamantaki, C. andAspirtakis, Y. \Optimal determination of rheologicalparameters for Herschel-Bulkley drilling uids and im-pact on pressure drop, velocity pro�les and penetrationrates during drilling", Journal of Petroleum Scienceand Engineering, 53, pp. 203-224 (2006).

35. Bailey, W.J. and Weir, S. \Investigation of methodsfor direct rheological model parameter estimation",Journal of Petroleum Science and Engineering, 21, pp.1-13 (1998).

36. Chen, Z., Ahmed, R.M., Miska, S.Z., Takach, N.E.,Yu, M. and Pickell, M.B. \Rheology and hydraulicsof polymer (HEC) based drilling foams at ambienttemperature conditions", SPE Journal, 12, pp. 100-107 (2007).

37. Hamida, T., Kuru, E. and Pickard, M. \Rheologicalcharacteristics of aqueous waxy hull-less barley (WHB)solutions", Journal of Petroleum Science and Engi-neering, 69, pp. 163-173 (2009).

38. Khalil, M., Jan, B.M. and Raman, A.A.A. \Rhe-ological and statistical evaluation of nontraditionallightweight completion uid and its dependence ontemperature", Journal of Petroleum Science and En-gineering, 77, pp. 27-33 (2011).

39. Arabloo, M. and Pordel Shahri, M. \Experimentalstudies on stability and viscoplastic modeling of col-loidal gas aphron (CGA) based drilling uids", Journalof Petroleum Science and Engineering, 113, pp. 8-22(2014).

40. Bjorndalen, N. and Kuru, E. \Stability of microbubble-based drilling uids under downhole conditions", Jour-nal of Canadian Petroleum Technology, 47(6), pp. 40-47 (2008).

41. Cardoso, J.J.F., Spinelli, L.S., Monteiro, V., Lomba,R. and Lucas, E.F. \In uence of polymer and surfac-tant on the aphrons characteristics: Evaluation of uidinvasion controlling", Express Polymer Letters, 4, pp.474-479 (2010).

42. Ahmadi, M.A., Galedarzadeh, M. and Shadizadeh,S.R. \Colloidal gas aphron drilling uid propertiesgenerated by natural surfactants: Experimental inves-tigation", Journal of Natural Gas Science and Engi-neering, 27, pp. 1109-1117 (2015).


43. Spinelli, L., Bezerra, A., Aquino, A., Lucas, E.,Monteiro, V., Lomba, R. and Michel, R. \Composition,size distribution and characteristics of aphron disper-sions", Macromolecular Symposia, 245/246, pp. 243-249 (2006).

44. Feng, W., Singhal, N. and Swift, S. \Drainage mecha-nism of microbubble dispersion and factors in uencingits stability", Journal of Colloid and Interface Science,337, pp. 548-554 (2009).

45. Zhao, J., Pillai, S. and Pilon, L. \Rheology of colloidalgas aphrons (microfoams) made from di�erent surfac-tants", Colloids and Surfaces A: Physicochemical andEngineering Aspects, 348, pp. 93-99 (2009).

46. MacPhail, W.F.P., Cooper, R.C., Brookey, T., Robin-son, R. and Paradis, J. \Adopting aphron uid tech-nology for completion and workover applications",Proceedings of SPE International Symposium and Ex-hibition on Formation Damage Control, Lafayette,Louisiana (2008).

47. Roy, D., Kongara, S. and Valsaraj, K.T. \Applicationof surfactant solutions and colloidal gas aphron sus-pensions in ushing naphthalene from contaminatedsoil matrix", Journal of Hazardous Materials, 42, pp.247-263 (1995).

48. Wan, J., Veerapaneni, S., Gadelle, F. and Tokunaga,T.K. \Generation of stable microbubbles and theirtransport through porous media", Water ResourcesResearch, 37, pp. 1173-1182 (2001).

49. Li, X., Thompson, J.G. and Liu, K. \Reduction ofamine emissions from an aqueous amine carbon dioxidecapture system using charged colloidal gas aphrons",US Patent No. 20160082384 (2016).

50. Jauregi, P., Gilmour, S. and Varley, J. \Characteri-sation of colloidal gas aphrons for subsequent use forprotein recovery", Chemical Engineering Journal, 65,pp. 1-11 (1997).

51. Arabloo, M. and Pordel Shahri, M. \E�ect of sur-factant and polymer on the characteristics of aphron-

containing uids", The Canadian Journal of ChemicalEngineering, 94, pp. 1197-1201 (2016).

52. Bjorndalen, N.N. \A study of the rheology, stabilityand pore blocking ability of aqueous", Ph.D. Thesis,Edmonton, Alberta (2010).

Biographies

Me'raj Heidari obtained his BS and MS degreesin Petroleum Engineering from the Department ofPetroleum Engineering, Ahwaz Faculty of PetroleumEngineering, Petroleum University of Technology, Iran.His research interests include preparations of drilling uids, and characterization and evaluations in the �eldof petroleum engineering.

Khalil Shahbazi is an Assistant Professor ofPetroleum Engineering in the Ahwaz Faculty ofPetroleum Engineering, Petroleum University of Tech-nology, Iran. His current research interests includeconventional and underbalanced drilling, drilling uidscharacterization, applications of �nite di�erence inwellbore ow modeling, rheology of non-Newtonian uids, and acidizing and hydraulic fracturing of wells.

Moslem Fattahi obtained his BS degree in Chem-ical Engineering in 2006 from Razi University, Ker-manshah, Iran, and his MS and PhD degrees in2008 and 2013 from the Department of Chemicaland Petroleum Engineering at Sharif University ofTechnology, Tehran, Iran. Now, he is an a AssistantProfessor of Chemical Engineering in the Abadan Fac-ulty of Petroleum Engineering, Petroleum Universityof Technology, Iran. His main research interests in-clude process modeling, reaction engineering, catalystsand nano-materials (mostly CNT and graphene-based)preparation, characterization and evaluations in the�eld of chemical engineering, petroleum re�ning, anddrilling engineering.

experimental study of rheological properties of aphron based drilling...

Documents