effect of oil contamination and temperature on the...

Proceedings THC-IT-2013 Conference & Exhibition

II-1

Effect of Oil Contamination and Temperature on the Resistivity of Drilling Mud

Ahmed S. Mohammed1 and C. Vipulanandan

2 and Richardson

3

Texas Hurricane Center for Innovative Technology

University of Houston, Houston, TX 77204-4003

Department of Civil and Environmental Engineering

Tel: 713-743-4278: E-mail: [email protected] 3Program Manager- RPSEA, Sugar Land, Texas, 77478

Abstract In this study, the changes in electrical resistivity of drilling mud with different percentage of bentonite

up to 8% with and without oil spill contamination was investigated. Also the effect of temperature up to

85 oC on contaminated and uncontaminated drilling mud was studied. Drilling muds were contaminated

up to 12% of oil (by total weight of drilling mud). The resistivity of contaminated and uncontaminated

samples using were measured using the resistivity meter and conductivity meter probe. The results

showed that the oil increased the resistivity of the drilling mud. Also the resistivity of uncontaminated

and contaminated drilling muds decreased with increasing the temperature. The effect of oil-

contamination on the resistivity of drilling mud was quantified.

1. Introduction

Drilling muds are fluids used to control formation pressures, lubricate and cool the bit, remove rock

fragments from the drilling well, and form a consolidated wall cake on the sides of the hole prior to

casing. These muds, which are highly viscous, are complex formulations and include such finely divided

materials as ground ilmenite, bentonite, various clays, barite, lead ore, fibers, hulls, etc. in a liquid

medium which may be aqueous (e.g., water or brine) or an oil Goodarznia et al. (2006). There are

several potential sources of oil leakage to the surrounding ecosystem through damaged pipeline,

discharges from coastal facilities, offshore petroleum production and natural seepage. Improper

management of used engine oil and illegal dumping of other hydrocarbon components could also

contaminate the drilling mud. Oil spillage or leakage will contaminate the soil and water system. Oil

contamination of the drilling mud could alter the rheological properties of oil-contaminated drilling mud

(Gozalpour et al. 1998).

2. Objectives

The objective of this study was to evaluate the effect of oil contamination on the resistivity of drilling

mud under different temperatures.

3. Materials and Methods

In this study, four different percentages of bentonite (2%, 4%, 6% and 8%) were used. The resistivity of

uncontaminated drilling mud was measured using the API resistivity meter and conductivity meter probe

under varying of temperature up to 85 oC. Drilling muds were contaminated using different percentage

of oil up to 12% (by total weight of drilling mud). Two different resistivity devices were used to

measure the resistivity of contaminated and uncontaminated drilling mud. API resistivity meter

accurately measures the resistivity of fluids, slurries, and semi-solids with resistivities from 0.01 to 400

Ohm-meters. Conductivity meter was also used to compare the results with conductivity from 0–19.99

µS; 20–199.9 µS/cm. Both of the devices were calibrated using standard solution of sodium chloride

(NaCl).

4. Analysis and Discussion

The resistivity of uncontaminated drilling mud was decreased by 34%, 54% and 69% when the bentonite

content changed from 2% to 4%, 6% and 8% respectively. Additional of 3% of oil (by total weight of

drilling mud) the resistivity increased for all the bentonite percentages. The resistivity of

mailto:[email protected]


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uncontaminated 2% bentonite drilling mud decreased by 50% when the temperature changed from 25 oC

to 85 oC. Based on the inspection of the test data for the properties investigated following relationships

is proposed.

(

)................... (1)

Where: = resistivity of drilling mud contaminated with oil, o = resistivity of uncontaminated drilling

mud, X= oil content (%), P and Q = model parameters. The model parameters were related to the test

variables as follows:

P or Q ML BXN ** for )2...(%.........0X

Where:

B= Bentonite content and N, L and M are model parameters.

5. Conclusions

Based on this study on oil contaminated drilling mud, the resistivity of the drilling muds was increased

by 56%, 51%, 57% and 63% for drilling muds with 2%, 4%, 6% and 8% of bentonite and contaminated

with 12% of oil respectively. For the uncontaminated 2% of drilling mud the resistivity decreased by

50% when the temperature was changed from 25 oC to 85

oC.

6. Acknowledgements

This study was supported by the Center for Innovative Grouting Materials and Technology (CIGMAT),

University of Houston, Houston, Texas with funding from DOE/NETL/RPSEA (Project 10121-4501-

01).

7. References

1. Gozalpour, F. and Heriot-Watt, U. (1998)." Determination of Reservoir Fluid Properties from

Samples Contaminated with Oil-Based Mud Filtrate" SPE 52062-STU, pp.1-3.

2. Goodarznia, I. and Esmaeilzadeh, F. (2006)." Treatment of Oil-Contaminated Drill Cuttings of

South Pars Gas Field in Iran Using Supercritical Carbon Dioxide" Iranian Journal of Science &

Technology, Transaction B, Engineering, Vol. 30, No. B5, pp. 607-611.

P R2 Q R

2

N 0.015

0.91

0.05

0.89 L -0.88 -0.01

M 3.1 0.9

0

2

4

6

8

10

12

14

16

18

0 2 4 6 8 10 12 14

Re

sist

ivit

y, (

Oh

m-m

)

Oil (%)

Bentonite=2% Bentonite=4% Bentonite=6%Bentonite=8% Model

Table 1. Model Parameters for Oil Contaminated Drilling Mud (X %> 0)

Figure 1. Relationship between Resistivity

and Oil Content for various Drilling Muds

Figure 2. Temperature Effect on 2% Drilling Mud

with Varying Amount of Contaminated Oil


II-3

Effect of Salt Contamination on the Fluid loss, Early Strength and Piezoresistive

Response of Smart Oil Well Cement A. Zomorrodian

1, C. Vipulanandan

1 and D. Richardson

2

1Center for Innovative Grouting Material and Technology (CIGMAT)

University of Houston, Houston, Texas 77204-4003

Tel: 713-743-4278: E-mail: [email protected] 2Program Manager – RPSEA, Sugar Land, Texas 77478

Abstract

Effect of salt contamination on the oil well cement slurry was investigated at room temperature. Results

showed that salt contamination increased the fluid loss, early compressive strength and also modified the

piezoresistive behavior of the oil well cement slurry. With 4% salt contamination, the initial resistivity

of the cement slurry was reduced by over 80%.

1. Introduction

Based on the location and zonal characteristics of the geological formation and/or during a hurricane,

there is a potential for contamination of the cement with salt during installation. Hence there is a need to

quantify the effect of salt contamination on the properties of oil well cement. This has led to many

studies on evaluating the impacts of salt contamination on different properties of fresh and hardened oil

well cement (Ismail et al 1993; Hunter 2010). Studies have shown the effect of salt contamination on the

mechanical, free water, rheological and thickening properties of cement. Hence there is a need for better

characterization the behavior of smart cement slurry contaminated with salt.

2. Objective

The objectives of this study are to investigate effect of salt contamination on the slurry and hardened

properties of smart oil well cement with enhanced sensitivity properties. Also of interest was the early

compressive strength and piezoresistive behavior of salt contaminated smart cement slurry.


All specimens were mixed based on API 10-B standard, at room temperature. Different tests were

performed on rheological, fluid loss, mechanical and electrical properties of up to 4% salt contaminated

modified cement slurries. Modified API fluid loss tests was performed at 100 psi at room temperature

and filtrate liquid was collected and measured at 1 minute intervals, until the blow out. Mechanical

properties were evaluated by measuring the 24 hour compressive strength and the piezoresistivity of

modified cement slurries.

4. Discussion and Results

As shown in fig.1, increasing salt concentration from 1% to 4% increased the 24 hour compressive

strength by 54% and 42%, respectively. Filtrate volume was increased up to 5% with the increasing the

salt content. Tests indicated that increased salt content reduced the electrical resistivity. Cement

electrical resistivity during the first 3 hours of curing was decreased up to 65% and 86%, with adding 1%

and 4% salt content, respectively. Piezoresistivity behavior of hardened cement slurries are shown in

Fig.2. Tests showed that increasing salt content to 1% increased the piezoresistivity property of

hardened cement.

5. Conclusion

Tests investigated the effect of salt contamination on the behavior of smart oil well cement. Due to salt

contamination the electrical resistivity reduced. With 4% salt contamination the resistivity was reduced

by over 80%. The early compressive strength and piezoresistive behavior were enhanced by salt



II-4

contamination. The changes in resistivity at failure for cement without and with salt contamination were

1.5% and 6% respectively.

6. Acknowledgement

This study was supported by the Center for Innovative Grouting Materials and Technology (CIGMAT)

with funding from DOE/NETL/RPSEA (Project 10121-4501-01).

7. References

Simao C. A., Miranda C.R., Vargas A.A., Pereira R. F. L., Santos R.L.L., Soares M.A.S., Conceicao

A.C.F. (2010). Cementing in Front of Soluble Salt Zones, Society of Petroleum Engineers. Doi:

10.2118/145719-MS

Ismail, S.A.A., Khalaf, F. (1993). Effectiveness of Low-Salt Cement Opposite Salt Bodies, Society of

Petroleum Engineers. Doi: 10.2118/25542-MS

Figure 1 – 24 hour compressive strength of class H cement slurries with salt concentration

Figure 2 - Effect of salt on the piezoresistivity behavior of of hardened oil well cement

0% Salt, 769.54

1% Salt, 1186.41 4% Salt, 1094.87

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

Ult

imat

e 2

4 h

ou

r co

mp

ress

ive

st

ren

gth

(p

si)

0%Salt

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

-0.01 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Co

mp

ress

ive

str

ess

(p

si)

ΔR/R0

0% Salt - 0.1% CF

1%Salt-0.1%CF


II-5

Fluid Loss Predication Using a New Filter Cake Model Aram M. Raheem

1, C. Vipulanandan

1 and D.Richardson

2

Texas Hurricane Center for Innovative Technology (THC-IT)



Email: [email protected], [email protected] Phone: (713) 743-4278 2Program Manager-RPSEA, Sugar Land, Texas 77478

Abstract: In this study, a new model was developed to predict the fluid loss in (6%) bentonite

drilling mud. In this model the hydraulic conductivity (permeability) of the filter cake was changing

with time. The new model predicated the experimental results very well.

1. Introduction

It is generally known in the petroleum industry that drilling muds have a more complex flow behavior

than Newtonian fluids, yet it is still common practice to express the flow properties of muds in terms of

a single viscosity. The drilling muds characterized as plastic materials which obey the laws of plastic

flow (Beck et al., 1947), or viscous materials where the viscosity change with the shear rate. When there

is loss of water from the drilling mud filter cake are formed. Based on the rate of fluid loss the formation

of filter cake will be affected and the permeability will vary with time. Based on the literature review the

permeability of the filter cake varied from 0.023 to 170 μd while the ratio of the solid volume fraction in

the filter cake to the mud varied from 3 to 4, (Elkatatny et al., 2012).

2. Objectives The objective of this study was to introduce the concept of permeability change with time in the filter

cake and compare it to the standard API infiltration equation. Both equations were compared with the

real laboratory values of infiltration through filter cake for 30 minutes.

3. Methods and Materials

In this study, 6% bentonite drilling mud was used. The fluid loss was measured using the API-filter test

equipment.

4. Model

The classical method to evaluate the infiltration through filter cake is given by the following equation

(Andrea et al. 2012):

√ (

) √

√ √

In the new model, it is assumed that the permeability of the filter cake changes with time and has the

relationship as follows:

Where: filter cake parameter β(1/min) depends on the type of drilling mud and rate of fluid loss. Hence,

the final form of the model will be as follows:

√ (

) √

√

√ √

mailto:[email protected],

mailto:[email protected],


II-6

Where:

,

,

,

,

5. Results

Both API and developed equation were used to verify experimental results of the fluid loss infiltration as

shown below:

Figure 1. Comparison of Fluid Loss Model vs. API Model with Experimental Results.

6. Conclusions

The proposed model showed a very good agreement with the experimental results in predicting the fluid

loss in the drilling mud.

7. Acknowledgement

This study was supported by the Center of Innovative Grouting Materials and Technology (CIGMAT)

with funding from DOE/NETL/RPSEA (Project 10121-4501-01).

8. References

1. Andrea S.V., Hau G.,Gerard D.B., Pavel B. and Pacelli L.J. (2012),”A CT Scan Aided

Core-Flood Study of the Leak-off Process in Oil-based Drilling Fluids”, SPE

International Symposium and Exhibition, Louisiana, USA, pp(1-25).

2. Beck R.W., Nuss W.F. and Dunn T.H.(1947), “The Flow Properties of Drilling Muds”,

Drilling Practice Journal, pp(9-22).

3. Elkatatny S.M., Mahmoud M.A. and Nasr-El-Din H.A. (2012),”Characterization of Filter

Cake Generated by Water-Based Drilling Fluids Using CT Scan”, SPE Drilling and

Completion Journal, pp(282-293).

0

5

10

15

20

25

30

0 1 2 3 4 5 6

Experimental Results

API,M=4.588

New Model,M=8.885

t1/2(min)

R2=0.97, fsc/fsm=1.8

R2=0.99, fsc/fsm=4,β=0.1

ko=170 m.d, p=80psi

Vf(

cm3)


II-7

Effect of Oil Contamination on the Electrical

Properties and Compressive Strength of Modified Oil Well Cement A. Khodaean

1 and C. Vipulanandan

1 , Ph.D., P.E. and D.Richardson

2

1Texas Hurricane Center for Innovative Technology (THC-IT)



E-mail: [email protected], [email protected] Phone: (713) 743-4278 2Program Manager-RPSEA, Sugar Land, Texas

Abstract

The effect of oil contamination on the modified oil well cement with and without metakaolin was

investigated. During this study, the portion of oil added into the cement mixture was 4 percent. The oil

contamination increased the resistivity of the slurry during the hydration of the cement and also affected

both the piezoresistive behavior and the compressive strength of the oil well cement.

1. Introduction

Over the past two decades, the amount of hydrocarbon contamination of cement has increased and has

resulted in damaging of the oil wells. Some sources of hydrocarbon contamination are oil spill, leaking

of petroleum from underground storage tanks, oil pipe vandalisation, drilling, and treatment activities for

exploration and production of hydrocarbons and hydrocarbon waste disposed from industries. Also

hurricanes can affect the oil spillage on the off Shore platforms [1]. Previous studies have been focused

on the effect of oil spill on the compressive strength of Portland cement but there is very limited

information on the electrical properties of oil well cement contaminated with oil. In this study the effect

of oil contamination on electrical properties and compressive strength of modified oil well cement class

H was investigated.

2. Objective

Main objective in this study was to investigate the oil contamination on the electrical properties of the

modified oil well cement, and also its effect on the compressive strength.


The cement was mixed with 10% metakaolin and then water was added. The water-to-cement ratio

(including Metakaolin) was 0.45 for both metakaolin and control specimen. 4% DTE oil as

contamination was added to both types of specimens, and then they were mixed for 1 minute and poured

in to the molds. Plastic cylinder molds of 2 inches in diameter and 4 inches in height were used. Each

mold had 4 wires installed to measure the electrical resistance.

4. Result and Discussion

As shown in Fig.1 adding 4% oil increased the initial resistivity by 30%, adding 10 metakaolin increase

resistivity by 35% and the mix had the combination of 10 % metakaolin and 4% oil increase the initial

electrical resistivity of the cement by 65%. From the Fig.2 it can be observed that control specimen with

1.8 ksi showed highest compressive strength and the mix with 4% oil contaminated showed the lowest

compressive strength of 0.65 ksi. Adding 10% metakaolin to the mix had 4% oil increased its

compressive strength up to 1.32 ksi. Both the control specimen and specimen made with 10%

Metakaolin and 4% oil inside showed the fractional change in resistance (ΔR/Rₒ) of about 0.5, while

specimen made with the 4% oil, reduced it to 0.1 at the failure point.




II-8

Fig.1. initial resistivity versus time Fig.2. Compressive strength versus fractional change in electrical resistivity

5. Conclusion

Resistivity can be used as a measurement to detect the contamination in the oil well. Also oil prevented

the cement from gaining strength and reduced its 2 days compressive strength up to 65%. Addition of

10% Metakaolin lowered this reduction by 27%. Also addition of oil as a contamination reduced the

sensing ability of cement mix, as it can be seen fractional change in resistance at failure for slurry with

and without oil was 0.1 and 0.5 respectively, while addition of 10 % metakaolin to contaminated sample

increase it to 0.5.

6. Acknowledgement


University of Houston, Houston, Texas with funding from the Ultra Deepwater Program

DOE/NETL/RPSEA (Project No. 10121-4501-01).

7. References

[1] Attom. M and Hawileh. R, “Investigation on concrete compressive strength mixed with sand

contaminated by crude oil products”, Construction and Building Materials 47 (2013) 99–103


II-9

Effect of Salt Contamination on the

Filtration Loss in 4% Bentonite Drilling Mud with Xanthan Gum B. Basirat

1, C. Vipulanandan

1 and D. Richardson

2




E-mail: [email protected], [email protected] Phone: (713) 743-4278 2Program Manager – RPSEA, Sugar Land, Texas 77478

Abstract

In this study the filter loss in drilling mud with contamination of salt (sodium chloride, NaCl) was

investigated. The drilling mud contained water, 4% bentonite and 0.5 lb/bbl (equivalent to 1.43 g/L)

xanthan gum [1]. 0.5% salt (sodium chloride, NaCl) increased the fluid loss by over 30%. Addition of

0.5% surfactant reduced the fluid loss of contaminated drilling mud by over 40%.

1. Introduction

Polymer with the name of “polysaccharide” is a class of materials made of a chain of thousands of

similar small unit molecules “monomers”. Xanthan gum is a high-molecular-weight biopolysaccharide

produced by bacterial growth. Commercially, this polymer is produced by growing the bacteria by a

fermentation process, precipitating the gum in alcohol, and then drying and milling the product to a

powdered form, then, it is added to a liquid medium to form the gum. The Xanthan gum Molecular

formula is C35H49O29 [2].

Xanthan gum has been used in drilling fluids, fracturing fluids, completion fluids and enhanced oil

recovery polymer floods [3]. Moreover, this polymer has been used as viscosities and fluid loss control

in oil and gas industry also can be used in almost any type of water and as a suspending agent [4, 5].

2. Objective

The main objective was to investigate (including fluid loss and changes in resistivity) the effect of salt

contamination on xanthan gum modified 4% bentonite drilling mud.


Three samples have been used: 1. Water, 4% bentonite and 0.5 lb/bbl (equivalent to 1.43 g/L) xanthan

gum (C35H49O29); 2. Water, 4% bentonite, 0.5 lb/bbl (equivalent to 1.43 g/L) xanthan gum (C35H49O29)

and 0.5% salt (sodium chloride, NaCl) and 3. Water, 4% bentonite and 0.5 lb/bbl (equivalent to 1.43

g/L) xanthan gum (C35H49O29), 0.5% salt (sodium chloride, NaCl) and 0.5% surfactant. The filter loss

and resistivity were measured.

4. Results and Discussion

It was found that presence of salt (sodium chloride, NaCl) or contamination increases the filtration of the

water based drilling fluid by 30%. Adding surfactant decreased the filter loss in salt contaminated

drilling mud about 40%. Presence of sodium chloride can be detected by measuring resistivity due to

influence of salt (sodium chloride, NaCl) on the increasing the conductivity. Therefore, by adding

sodium chloride the resistivity decreased by 86%, after adding surfactant the changes in resistivity was

doubled.

5. Conclusion

Based on this study contamination increases the filter loss about 30% and decreased the resistivity by 86%

compared to the sample with no contamination. Adding surfactant improved this filtration considerably

(about 40%) while the resistivity got doubled compared to contaminated drilling mud.



II-10

Figure 1:Filter loss of three samples

Figure 2: Resistivity of three samples

6. Acknowledgements


University of Houston, Houston, Texas with funding from the Ultra Deepwater Program

DOE/NETL/RPSEA (Project No. 10121-4501-01).

7. References [1]. Khan, R., Kuru, E., Tremblay, B. and Saasen, A. (2003), “An Investigation of Formation Damage Characteristics of

Xanthan Gum Solutions Used for Drilling, Drill-In, Spacer Fluids, and Coiled Tubing Applications” Canadian International

Petroleum Conference, Calgary, Alberta, Canada, June 10 – 12.

[2]. Cohan, Wendy. "Could Xanthan Gum Sensitivity be Complicating your Celiac Disease Recovery?". Celiac.com.

Retrieved 2010-05-19.

[3]. Chatterji, J. and Borchardt, J.K., (1981) Application of water soluble polymers in the oil field. Journal of Petroleum

Technology, 2042-2054 (November).

[4]. Jayanth T. Srivatsa, B.E, August, ٢٠١٠, "An Experimental Investigation on use of Nanoparticles as

Fluid Loss Additives in a Surfactant – Polymer Based Drilling Fluid", Submitted to the Graduate

Faculty of Texas Tech University in Partial Fulfillment of

The Requirements for the Degree of MASTER OF SCIENCE

[5]. Carico, R.D. and Bagshaw, F.R.: "Description and Use of Polymers Used in Drilling, Workovers, and Completions,"

paper SPE 7747 presented at the 1978 SPE-AIME Production Technology Symposium, Hobbs, N.M., Oct. 30-31.

0

2

4

6

8

10

12

14

0 5 10 15 20 25 30

Filt

er L

oss

(m

L)

Time (min)

Filter press test 4% Bentonite + 0.5 lb/bbl or 1.43 gr/Liter Xanthan gum

4% Bentonite + 0.5 lb/bbl or 1.43 gr/Liter Xanthan gum + 0.5% NaCl

4% Bentonite + 0.5 lb/bbl or 1.43 gr/Liter Xanthan gum + 0.5% NaCl + 0.5% surfactant

0

1

2

3

4

5

6

7

8

4% Bentonite + 0.5 lb/bblXanthan gum

4% Bentonite + 0.5 lb/bblXanthan gum + 0.5% NaCl

4% Bentonite + 0.5 lb/bblXanthan gum + 0.5% NaCl +

0.5% surfactant

Res

isti

vity

(Ω

.m)

Resistivity

http://www.celiac.com/articles/21710/1/Could-Xanthan-Gum-Sensitivity-be-Complicating-your-Celiac-Disease-Recovery/Page1.html


II-11

Effect of Lime on Modified Oil Based Drilling Mud (OBM) Dongmei Pan

1, C. Vipulanandan

1 and D. Richardson

2




Tel: 713-743-4291: email: [email protected] 2RPSEA, Program Manger, Sugar Land, Texas

Abstract

In this study, the effect of lime contamination from the formations on a modified oil based drilling

mud(OBM) was investigated. Adding 0.5% surfactant (sodium dodecyl sulphate, SDS) substantially

reduced the resistivity of the OBM. Contamination with lime not only increased the pH but also changed

the electrical resistivity. With 2% lime contamination the electrical resistivity increased by over 1300%.

1. Introduction

Oil based drilling muds contain a mixture of an oil-base fluid and an aqueous-brine fluid and the typical

ratio is approximately 3. Oil-based mud systems are widely used in many deep-water environments,

particularly systems where unconsolidated sediments and swelling clay minerals are common. Main

advantage of OBM over a water based mud is that the external phase (oil) coats and protects metal

surfaces of the drilling equipment to minimize corrosion from H2S and CO2, Another important

advantage is that free lime, Ca(OH)2, can be carried in an oil mud to neutralize an influx of these acidic

gases (Garrett1988; Adebayo, 2011). Calcium salts are sufficiently soluble in water/drilling mud to

cause problems with clay flocculation. The pH of the solution also affects the solubility of many

thinners and divalent metal ions such as calcium and magnesium, and influences the dispersion or

flocculation of clays (Chaney 1942). Maintaining an excess pH controlling agent is particularly

important for some fluid system because these systems will lose all rheological properties if the pH was

allowed to drop to less than 7 ( Robert 2004). The control of many drilling fluid system properties is

dependent on pH. Moreover, the pH of drilling mud is controlled in range of 8.5-10 for corrosion

prevention of drilling device and good behavior.

2. Objectives

The overall objective was to investigate the effect of lime contamination on the resistivity of OBM. Also,

the change in the pH of OBM with varying percentages of lime was investigated.

3. Material and methods

In this study, oil based drilling mud samples were prepared by mixing by vegetable oil, bentonite, water

and Ca(OH)2. The ratio of oil to water was 4: 1. Five 4% of bentonite drilling mud samples were

prepared. OBM without any additive was the control sample. The rest four samples were mixed by

adding 0.5% surfactant and different amount of Ca(OH)2 under room temperature (Table1). And, the

resistivity of all of samples was measured using a conductivity meter for one hour after mixing it for 60

seconds.

Table 1 Summary of the Test Results

Sample

No.

Formulation Measurement

Oil:Water

(by Vol.)

Bentonite

(% by wt.) Surfactant(%) Lime(%) PH

Resistivity

mean (Ω·m)

Sample 1 4 4.0% 0.0% 0.0% 8.2 43687.3

Sample 2 4 4.0% 0.5% 0.0% 9.5 30.8

Sample 3 4 4.0% 0.5% 0.5% 11.8 28.2

Sample 4 4 4.0% 0.5% 1.0% 12.3 68.1

Sample 5 4 4.0% 0.5% 2.0% 12.1 375.1



II-12

Figure 1. Relationship of pH and Resistivity of OBM with Surfacant and Lime

4. Results and discussion

As summarized in Table 1, for the Sample 1 with oil, water and bentonite, the mean resistivity was very

high and was about 43687 Ω·m. Adding 0.5% surfactant (SDS), the resistivity of Sample 2 decreased

sharply to 30.8 Ω·m. Also, surfactant changed the pH of OBM from 8.2 to 9.5. For Sample 2 and 3, the

resistivity after contaminating with 0.5% lime were 30.8 Ω·m and 28.2 Ω·m respectively, and the pH

changed from 9.5 to 11.8. It indicated a certain percentage of lime can control pH well in oil based mud

as a pH agent. But the resistivity of Sample 5 increased with the addition of more lime (2%) compared

to Sample 3 and 4. With 2% lime the modified OBM resistivity in Sample 5 was increased. From

observation, Samples 5 had more free oil because aggregation happened, resulting in increase in

resistivity.

5. Conclusion

Oil based mud (OBM) consistency was improved by adding surfactant (sodium dodecyl sulphate, SDS)

and it reduced the electrical resistivity substantially compared to the sample without surfactant.

Contamination of over 0.5% of lime increased the electrical resistivity of the OBM.

6. Acknowledgement

This study was supported by CIGMAT with funding from DOE/NETAL/RPSEA Project 10121-4501-01.

7. Reference

1). Chaney (1942), “A review of recent advances in drilling-mud control”, Drilling and Production

Practice, presented at Twenty-third Annual Meeting, Chicago, Nov.1942

2). Elsen, M. and Broussardand, L. (1991), “Application of a lime-based drilling fluid in a high-

temperature/high-pressure environment”, SPE Drilling Engineering, March 1991.

3). Garrett, R.L.,Carlton, L.A.,and Denekas, M.O.,(1988) Methods for Field Monitoring of Oil-Based

Drilling Fluids for Hydrogen Sulfide and Water Intrusions, SPE Drilling Engineering, Vol.3, No.3

PP.296-302, 1988

4). Adebayo, T. A, Balogun O., Igweze A. and Oluwaseyi, H. (2011) “Alteration of Oil-Based Drilling

Mud properties due to contact with CO2 gas kick during drilling,” Asian Transactions on Engineering

(ATE ISSN: 2221-4267) Vol. 01, Issue 04, Sep. 2011

43687.3

30.8 28.2 68.1 375.1 0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

Sample1 Sample 2 Sample 3 Sample 4 Sample 5

Res

isti

vit

y(Ω

·m)

Sample no.


II-13

Comparing the Year 2013 Hurricane Predictions for

Gulf Coast and Texas Dongmei Pan and C. Vipulanandan, PhD., P. E.




Tel: 713-743-4291: email: [email protected]

Abstract: It is a challenge to predict the number of hurricanes expected during the hurricane season.

Total hurricanes for 2013 in the Atlantic region predicted by the Colorado State University (CSU),

Florida State University (FSU) and National Oceanic and Atmospheric Administration (NOAA) varied

from 7-11. Based on THC-IH prediction, the probability of one hurricane for the Gulf of Mexico and

Texas in 2013 varied from 17.6% to 36.8% and 30.2% to 36.8% respectively.

1. Introduction

Several institutions keep predicting the hurricane probability and total number for the Atlantic hurricane

season each year. CSU has been predicting hurricane for the past 30 years. The CSU Tropical

Meteorology Project has made forecast of the upcoming season’s Atlantic basin hurricane activity. Its

research team has shown that a sizable portion of the year-to-year variability of Atlantic tropical cyclone

(TC) activity can be hindcast with skill exceeding climatology. This year’s June forecast was based on a

statistical methodology derived from 30 years of past data. The Center of FSU for Ocean-Atmospheric

Prediction Studies (COAPS) in the College of Arts and Sciences was officially formed in August 1996

by the Florida Board of Regents. COAPS is a center of excellence performing interdisciplinary research

in ocean-atmosphere-land-ice interactions to increase our understanding of the physical, social, and

economic consequences of climate variability. The Texas Hurricane Center for Innovative Technology

(THC-IT) has developed in a hurricane prediction model based 162 years of data with a Poisson

distribution and started to predict hurricane for Gulf of Mexico (GOM) and every state along GOM

since 2009. Total hurricane in the year 2012 predicted by CSU, FSU and NOAA varied from 4 to 8. For

year 2012, THC-IH predicted probability of no hurricane for Texas and GOM varied from 6.6%-70%

and 1.8%-53% respectively, and there was no hurricane in Texas or GOM. The Climate Prediction

Center (CPC) at NOAA predict the climate variability, real-time monitoring of climate and the required

data bases, and assessments of the origins of major climate anomalies.

2. Objectives

The objective was to review and summarize the hurricane predictions by the CSU, FSU and NOAA for

2013 Atlantic hurricane season. Also the probabilities of hurricanes predicted by the THC-IH for Texas

and Gulf Coast of the United States in 2013 are compared to other predictions.

3. Analyses

Hurricane prediction by CSU, FSU, NOAA for 2013 Atlantic hurricane season are summarize in Table 1

with remarks (TNS-total number of storms; H-number of hurricanes).Compared to the actual hurricane

number in the past four years, the predictions were either higher or lower than the actual number of

hurricanes. For 2013, the number of hurricanes varies from 7-11. The Frequency of Hurricane per year

as estimated by THC-IT using f(h)=exp(-λ)xλ^h/h!; (h=0,1,2,…), where h is the number of hurricane per

year, λ is the expected number of hurricanes during a year. By analyzing 162 data (1851-2012) from

NOAA, the parameter λ for Texas and the Gulf Coast of the United States were 0.36 and 1.1. It means

the probability for hurricane in Texas and the Gulf Coast of the United States is 0.36 and 1.1 each year

respectively. The probability of h hurricanes occurring in T years is, f(h| λ, T)=exp(-λT)x(λT)^h/h!;

(h=0,1,2,…), prediction of hurricane probability in 2013 is based on different year cycles (T = 1,2,...

,10) simulation and calculations (Liu and Vipulanandan,2010; Elsner and Bossak,2001).



II-14

Table 1 Hurricane Prediction of Atlantic Hurricane Season by FSU, NOAA, and CSU

(TNS: Total Named Storms, H: Hurricane)

Year FSU NOAA CSU

Actual

number Remark

TNS H TNS H TNS H H

2013 15 8 13 - 20 7-11 18 9 unknown unknown

2012 13 7 70% chance of

9-15

70% chance of

4-8 10 4 10

Lower than real

number

2011 17 9 12-18 6−10 16 9 7 close to real number

2010 17 10 14-23 8−14 18 10 12 close to real number

2009 8 4 9−14 4−7 11 5 3 close to real number

Figure 1 Actual Hurricanes and Probability Predicted by THC for the past decade (a) Texas and (b) U.S.

Gulf Coast

4. Conclusions

According to the prediction by CSU, FSU and NOAA, 2013 Hurricane numbers varied and between 7

and 11. Based on the past 162 years of data, predictions by THC-IH for hurricane in the last three years

have been good. The frequency of hurricanes in Texas and Gulf Coast of the United States was 0.36 and

1.1 per year. The probability of one hurricane in Texas varied from 17.4 to 36.8%. The probability of a

second hurricane varied from 4.4% to 27%. The probability of zero hurricanes in U.S Gulf Coast varied

from 1%-58.7% this year. The probability of one hurricane along the Gulf of Mexico varied from 30.2%

to 36.8%. The probability of a second hurricane varies from 8.4% to 27%.

5. Acknowledge

The study was supported by the THC-IT (http://egr.uh.edu/hurricane) with funding from various

industries.

6. References

[1] Liu, M. and Vipulanandan, C. (2010) “Prediction the Hurricane Probability of 2010 In the Gulf

Coast of the United States ”, Proceedings, THC 2010 Conference, Houston, Texas.

[2] Elsner, B. J. and Bossak, H. B. (2001) “Bayesian Analysis of U.S. Hurricane Climate”, Journal of

Climate, 14, 4341-4350.

(a) (b)

http://egr.uh.edu/hurricane


II-15

Effect of Oil Contamination on the Behavior of a 6% Bentonite Drilling Mud

K. Ali1, C. Vipulanandan

1 and Donald Richardson

2

1Center for Innovative Grouting Materials and Technology (CIGMAT)



Email: [email protected], [email protected] Phone: (713) 743-4278

Program Manger –RPSEA, Sugar Land, Texas 77478

Abstracts

The effect of oil contamination on the plastic viscosity and electrical resistivity of bentonite drilling mud

(6% w/w) was investigated.The oil content in the mud was varied up to 3%. The plastic viscosity was

reduced and the electrical resistivity was increased with increase in oil content.

1. Introduction

During construction of oil wells, there are many challenges (natural disasters, accidents etc.) that may

results in the contamination of the drilling mud. The grounding of a crude oil carrier ‘Metula’ in the

strait of Magellan in August 1974 resulted a loss of 52000 tons of crude oil spread over 250 km of

shoreline (Marine Pollution Bulletin, 1978). Deepwater Horizon disaster caused 60 miles of shoreline in

Alabama contaminated with crude oil (Hayworth et al. 2011). The shorelines are subjected to diurnal

tide which potentially can cause the nearby rivers, channels and lake water to be affected with the spilled

oil. Any drilling activity near these areas can be affected by the spilled oil while preparing the drilling

muds. In order to advance monitoring technology, it is critical to quantify the changes in the bentonite

drilling muds due to spilled oil contamination.

2. Objectives

To study the effect of oil contamination on the resistivity and plastic viscosity of 6% (w/w) bentonite

drilling mud.


Commercially available bentonite was used with water to prepare the drilling mud. Various amount of

oil (used engine oil) was added to determine the effect on the mud properties. Fann Viscometer was used

to determine the plastic viscosity and to determine the resistivity, conductivity meter was used which

gives the conductivity of the drilling mud (Figure 1).

Fann Viscometer Conductivity Meter

Figure 1. Fann Viscometer and Cponductivity meter

After determining the conductivity of the drilling mud, the resistivity was determined from the

relationship, Resistivity = 1/Conductivity.


4.1 Oil on viscosity: Plastic viscosity of a 6% (w/w) bentonite mud with different percentage (0 to 3%

w/w) of oil content was determined with a Fann viscometer. Result (Figure 2) showed that oil had a

tendency to reduce the plastic viscosity of bentonite mud. Viscosity was reduced by about 30% with an

addition of 1% oil.


II-16

4.2 Oil on resistivity: Figure 3 shows the effect of oil on the resistivity of bentonite drilling mud. The

resistivity is sensitive to the oil content. An addition of 2% (w/w) oil increased the resistivity by 20%.

Figure 2. Effect of oil on the plastic viscosity of a 6% bentonite mud.

Figure 3. Effect of oil on the resistivity of a 6% bentonite mud

4.3 Relationship between resistivity and plastic viscosity A relationship between the resistivity and

the plastic viscosity was determined from the experimental data and shown in Figure 4. Based on the

limited data, a linear relationship is proposed as follows: μ = Aρ + B ……………..……(1)

Where, μ = Plastic viscosity (cP), ρ = Resistivity (Ohm-m), A and B are constants.

From this investigation, A was found as -2 (cP/Ohm-m) and B was found to be 30 cP. And the

coefficient of determination R2 = 0.91

Figure 4. Relationship between the resistivity and the plastic viscosity

5. Conclusions

1. Oil reduced the plastic viscosity of 6% bentonite drilling mud.

2. Oil increased the resistivity of bentonite drilling mud. An addition of 2% oil increased the

resistivity of the drilling mud by about 20%.

3. The relationship between the resistivity and the plastic viscosity was found to be linear.

6. Acknowledgements This study was supported by the Center for Innovative Grouting Materials and

Technology (CIGMAT), University of Houston, Houston, Texas with funding from the Ultra Deepwater

Program DOE/NETL/RPSEA (Project No. 10121-4501-01).

7. References

1. Coastal oil spill impact assessed. Marine Pollution Bulletin, 1978, Volume 9, Issue 4, pp. 87 – 88

2. J. S. Hayworth, J.S., Clement, T. P., and Valentine, J. F. 2011. Deepwater Horizon oil spill impacts on

Alabama beaches. Hydrology and Earth System Science, 15, 3639–3649

0

10

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)

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stic

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cosi

ty (

CP

)

Resistivity (Ohm-m)


II-17

Low-Power Optical Switching for Hurricane Resilient Communication

Linsen Wu, Wenhao Chen, Dmitriy Chenchykov, Lei Wang, Yuhua Chen*

Systems and Research Laboratory

Department of Electrical and Computer Engineering

University of Houston

Houston, TX 77204-4005

* Email: [email protected]

Abstract This paper describes the prototyping effort of a low-power optical switching router which

provides hurricane resilient communication. The proposed optical switching network can operate on

backup powers during Hurricane power outage. FPGA hardware is built and the result is demonstrated

in a network testbed with multi-party communication applications.

1. Introduction

Hurricanes usually cause damages to the transportation and power systems as well as expose regions to

the threat of diseases. In order to handle emergency situations, a resilient and reliable telecommunication

network would be very critical. However, during the hurricanes, the power systems are usually

destroyed by the extreme weather, which blocks the regular communication channels. In this paper, a

method that can keep low power consumption for optical switching and zero power for the default

optical path is proposed based on the Reconfigurable Asymmetric Optical Burst Switching (RA-OBS)

networks [1]. The proposed approach is implemented in the hardware tested.

2. Methodology

A dual-mode scheduling approach is proposed in this paper. In normal situations, a standard

configuration is applied on the entire system, which means the optical signals can be switched in normal

ways. In this mode, an integrated multi-mode scheduling approach is used as shown in Figure 1. The

multi-mode channel selection and channel update unit can be shared among all three functions: burst

scheduling in the optical burst switching (OBS) mode, connection setup/teardown in the optical circuit

switching (OCS) mode, and channel reconfiguration in the electronic packet switching (EPS) mode. The

proposed approach provides an integrated solution to the problem as well as enables dynamic

wavelength sharing among different switching modes. In emergency situations such as main power

down due to Hurricane, the scheduler changes the mode of the system to the low-power configuration,

which means that backup batteries are used to drive the low power micro electro mechanical systems

(MEMS) switches to implement optical signals switching. In the default path, the MEMS switches do

not need any power to keep the default configuration, which will lead to zero energy consumption in

passing optical signals in the core and low power consumption in the edge.

3. Simulation and Hardware Experimental Results

Both the traditional LAUC-VF scheduling [2] and the proposed integrated multi-mode scheduling are

simulated for the optical signals using a 14-node,

21-link topology. Each optical link carries 8 data channels and 2 control channels at 1 GB/s in each

direction. Every node sends traffic to all node and the bursts arrival follows a Poisson process with

average burst size is 70 Kbytes. The result shows that although RA-OBS does not have full wavelength

conversion capability, the proposed integrated scheduling delivers blocking performance close to full

conversion LAUC-VF for relatively large number of electronic ports. This is because integrated


II-18

scheduling can efficiently utilize the pool of E/O and O/E converters shared by multi-mode traffic. In

addition to software simulation, the effectiveness of the proposed integrated multi-mode scheduling

algorithm has been verified, and its speed and cost effectiveness in hardware implementation in a

hardware testbed. The proposed algorithm is implemented in FPGA hardware using Hardware

Description Language Verilog HDL. The FPGA hardware is used along with the optical switching node

in the optical switching testbed. A large medical image transfer hardware experiment is demonstrated to

test the reliability of the MEM switch. Figure 2 shows the system architecture and topology of the

experiment. More specifically, three routers are in the same subnet while router 1 and router 2 are

isolated by customer

VLAN tag from router 3. Server connected to 3Com switch streams two separate medical images traffics

simultaneously each at the speed of 100 Mbps. The experiment swaps the SVLAN tag by routing the

traffic to FWCDS1 and FW9500. At the egress port, clients get the traffic coming out from FWCDS2

and TVs display a portion of the high resolution medical images at both the client. On the server side,

iPads dynamically setup and teardown the optical path by sending commands to DE3 FPGA board,

which configures the optical switch upon receiving of correct command. By zooming or moving the

miniature of medical images in the iPad application, server recalculates the position of current image

and continuously streaming traffic to the clients depending on the availability of the optical path

between server and clients.

Figure 1: Integrated Multi-Mode Scheduler

OBS Burst

Scheduling

OCS Connection

Setup/Teardown

EPS Mode

Reconfiguration

Multi-Mode

Channel

Select

Multi-Mode

Channel

UpdateCo

ntr

ol P

ack

et P

re-P

roce

sso

r

Control Packet Post-Processor

Integ

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han

nel S

tatus

Control

Packets

Out

Switching

Configurations

Co

ntr

ol

Pack

ets

In

Integrated Multi-Mode Scheduler


II-19

Figure 2: System architecture of medical image transfer experiment

4. Conclusion

In this paper, a dual-mode scheduling scheme for the optical burst switching network is proposed. The

scheme can provide burst scheduling in the OBS mode, connection setup/teardown in the OCS mode, as

well as channel reconfiguration in the EPS mode in an integrated fashion in both normal and emergency

situations. The performance of the proposed integrated scheduler has been verified using OBS-ns2

simulator as well as in a hardware testbed. More specifically, the algorithm is implemented on FPGA

hardware in an optical switching testbed. The result demonstrated in real hardware shows that the

proposed algorithm can make adjustment according to environmental factors and switch between the

normal mode and the emergency mode. All these results are based on low power passive optical

switches and couplers that can be used in hurricanes and other extreme weathers.

5. Acknowledgement

This work was supported in part by the National Science Foundation (NSF) under Grant CNS-0708613,

0923481, 0926006, and the Texas Advanced Research Program (ARP) under Grant G096059.

6. References

[1] Y. Chen, W. Tang, “Concurrent DWDM Multi-Mode Switching: Architecture and Research

Directions,” IEEE Communications Magazine, vol. 48, no. 5 (2010).

[2] Y. Xiong, M. Vandenhoute, H. C. Cankaya, “Control architecture in optical burst-switched WDM

networks,” IEEE Journal on Selected Areas in Communication, vol. 18, Oct. 2000, pp. 1838–1851.

OU

T I

N

FWCDS-2

FWCDS-1

OU

T I

N

OUT IN

… ……

IN OUT

OU

T I

N

OU

T I

N

loopback

IN OUT

Internal

connection

OU

T I

N

SVLAN: 4

SVLAN: 4

SVLAN: 3

Rv Tx

Rv Tx

Tx Rv

SVLAN: 3

crossover connection

CVLAN-2

server

CVLAN-1 router 1 router 2

iPad 1: (dhcp) iPad 2: (dhcp)

3Com switch

IFP5-EXX1 IFP5-ETA1(1-5) WS2A

WMP5-W8A1 WMP5-ASC1

Tx Rv

PC1: (dhcp)

PC2: (dhcp)

TV1

TV2

FW9500

router 3

RJ-45

DE3 Reconfigurable

switch

…


II-20

Characterizing the Behavior of Modified Cement

Contaminated with Oil Based Drilling Mud

M. Heidari1 and C. Vipulanandan

1, Ph.D., P.E. and D. Richardson

2




Email: [email protected], [email protected] Phone: (713) 743-4278 2Program Manger –RPSEA, Sugar Land, Texas 77478.

Abstract

In this study contamination of modified cement with oil based muds (OBM) was investigated. Electrical

resistivity was used as a monitoring tool to capture the contamination of cement with up to 5% OBM.

The results indicated that increased mud contamination, increased the electrical resistivity of the slurries,

and reduced the 1-day compressive strength of the cement. A linear correlation was obtained between

the 24 hour change in electrical resistivity and the compressive strength of the contaminated samples.

1. Introduction Oil based muds (OBM) contamination can have a severe impact on cement performance in wellbores.

This occurs when cement and OBM become mixed during normal well cementing operations or during

disaster conditions. Contamination of cement with OBM will compromise the integrity of well cement,

and cause disastrous failures (Harder and Carpenter 1993). Hence, there is a need to monitor the well

cement during placement and operation to determine if it is contaminated with OBM. Harder and

Carpenter (1993) laboratory tests indicate that OBMs, even at very low concentrations are extremely

detrimental to cement performance

2. Objective The main objective of this study was to quantify the contamination of well cement with oil based muds

by monitoring its electrical resistivity during curing. Also to investigate the effect of OBM

contamination on short-term compressive strength of cement.

3. Materials and Methods Class H cement was modified with conductive fillers and was prepared according to the API procedure

with water to cement ratio of 0.38. To contaminate the cement, 1 to 5% percent of vegetable oil based

mud was mixed with cement. Electrical resistivity was measured continuously by the developed data

acquisition system during 24 hours of curing age as shown in Fig. 1. Standard compression test was

done to determine the contaminated cement strength development after 1 day.

Figure 2. The developed data acquisition unit apparatus for measuring the electrical resistivity


II-21

4. Results and Analysis As shown in Fig. 2, the initial electrical resistivity of the cement increased with the mud contamination.

Since the electrical resistivity of oil based muds is higher than that of cement, the contaminated

specimens exhibited higher initial resistivity. As cement hydrates, electrical resistivity response

characterizes the behavior of curing cement. In this experiment, short term resistivity response of

samples showed that initially after mixing cement with water, resistivity decreased to a minimum point

which is due the presence of mobile ions in the liquid phase. With the formation of solid hydration

products, resistivity increased rapidly and after that, increase was at a lower rate. Change in electrical

resistivity with respect to minimum resistivity, quantifies the decrease in porosity and other property

development. The 1-day compression test results showed that mud contamination degraded the

compressive strength of cement. A summary of electrical resistivity measurement and compressive

strength of the samples are provided in table1. A linear correlation was obtained between 1-day

electrical resistivity change and 1-day compressive strength which is shown in Fig 3.

Table 1. Summary of electrical resistivity response of the uncontaminated and OBM contaminated

samples

ρ-initial (Ω-m) ρmin(Ω-m) ρ24 (Ω-m) (ρ24-ρmin)/ρmin Compressive strength (Ksi)

Cement 1.15 1.04 1.66 59% 1.41

Cement+1%OBM 3.35 2.96 4.47 51% 1.28

Cement+5%OBM 3.85 3.43 4.53 32% 0.32

5. Conclusions

(1) Addition of 1% and 5% OBM to modified cement increased its initial resistivity more than 290%

and 330%, respectively.

(2) OBM contamination roughly reduced the 1-day compressive strength of cement.

(3) Electrical resistivity change linearly correlated with the 1-day compressive strength of cement.

6. Acknowledgment

This study was supported by CIGMAT with funding from DOE/NETL/RPSEA (Project 10121-4501-

01).

7. References

C.A. Harder and R.B. Carpenter, “Optimization of oil-base mud chemistry for cementing”, IADC/SPE

025183 presented at the Drilling Conference, Los Angeles, CA, March 1993.

Figure 2. Initial electrical resistivity of specimens Figure 3. Change in resistivity vs. compressive strength

Cement 1% OBM

5% OBM


II-22

Axial and Lateral Sliding of Pipe on Simulated Soft Soil Seabed Mohammad Sarraf. J and C. Vipulanandan, Ph.D., P.E.




Email: [email protected], [email protected], Phone: (713) 743-4278

Abstract: Deep-water oil pipelines rest on very soft seabed and are susceptible to axial and lateral

movements which are heavily dependent on the pipeline penetration at every stage. Hence, predicting

the initial embedment of pipeline after installation or any major changes in the seabed (in our case,

severe earthquake) is one of the important design considerations for the bottom stability analysis.

Lagrangian Finite element technique with mesh refinement was used to model the pipe soil interaction

in the soft soil. The pipe was modeled in Lagrangian and the soil was modeled in Eulerian framework.

1. Introduction.

Offshore pipe embedment is a large deformation problem. Various techniques have been proposed in the

past to overcome numerical difficulties in large strain finite element modeling, which include updated

Lagrangian, updated Eulerian, pure Eulerian, mesh free and Arbitrary Lagrangian Eulerian, (Wang,

2010). Simulated pipe embedment using remeshing and interpolation technique with small strain

(RITSS) and recently implemented Coupled Eulerian Lagrangian (CEL), (Dutta, 2012). In this approach

material flow through the fixed mesh and therefore there is no meshing issue at large deformation.

2. Objective

The main focus of this study was to conduct FEM analysis on pipe subjected to vertical loading (self-

weight) and lateral loading (earthquake) and investigate the vertical penetration of pipe on a very soft

soil. Determine the dynamic force displacement response of a typical PIP subsea pipeline after the

laying procedure and after dynamic displacement of soil due to an earthquake in the horizontal direction.

3. FEM Formulation and Parameter Selection

A steel pipe of 0.8 m diameter (D) was modeled in this study. To model the soil an Eulerian domain of 8

m × 4.5 m× 0.04 m (width × height × t thickness) was used(Fig.1) the soil was modeled as an elastic

perfectly plastic material. Eu=500su0 and poison’s ration is taken as 0.49 with a unit weight of 1620

for clay. In this study the numerical analyses was divided into four steps. The first step is the geostatic

step. During the geostatic step pipe is kept outside the Eulerian part and the gravity and geostatic force

applied to pipe. In the second step, the pipe is moved downward in given velocity to the seabed. Since

this movement occurs only through the void, no reaction forces observed during this step. In the third

b

Figure 1.Finite Element model used in this study


II-23

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0 2 4 6

𝑾/𝑫

Time (s)

Onset of Earthquake Excitation

step, pipe starts to penetrate into the seabed due to gravity load. And the analyses shifts from

displacement control to force control. Simultaneously, a cyclic lateral movement due to the vessel

movement during the installation applied to the pipe. In the fourth step earthquake acceleration in the x

direction using the amplitude option for the duration of 2 second was applied at the bottom of Eulerian

part. In parallel, a fully displacement controlled analyses was conducted to measure force displacement

response of pipe over subsea seabed.

4. Result and Discussion

5. Conclusion

Combined Eulerian –Lagrangian approach can be used to model the pipe behavior in soft soil.

6. Reference

1. D.J. White, U. o. W. A. (. U. o. C. et al., 2011. SAFEBUCK JIP - Observations of Axial Pipe-soil

Interaction from Testing on Soft Natural Clays. Offshore Technology Conference,.

2. G.M. Wantland, W.-C. C., M.W. O'Neill, U. o. H., L.C. Reese, U. o. T. a. A. & and E.H. Kalajian, F.

I. o. T., 1979. Lateral Stability Of Pipelines In Clay. 3. Harald Brennodden, S. a. A. S. N. N. S., 1992. Time-Dependent Pipe-Soil Resistance for Soft Clay. Offshore

Technology Conference,.

4. J.M. Schotman, K. E. L. a. F. S., 1987. Pipe-Soil Interaction: A Model for Laterally Loaded Pipelines in Clay.

ffshore Technology Conference, p. 8.

Figure3. a) Normalized Force (V) – Displacement (W) response in Pure Lagrangian Analyses for Displacement control with ALE

meshing. b) Penetration Vs. time during installation and Earthquake loading in Coupled Eulerian Lagrangian Analyses (CEL) and at

loading control stage.

(a)

(b) (a)

Figure2. Vertical Pipe penetration (Eulerian) a) Subjected to installation force b) After Earthquake Excitation

(b)


II-24

Modified Ultrafine Cement as Piezoresistive Repair Material for Damaged Oilwell

Structures P. Ramanathan and C. Vipulanandan

Center for Innovative Grouting Materials and Technology (CIGMAT)



Email: [email protected], [email protected] Phone: (713) 743-4278

Abstract

Using modified ultrafine cement to repair damaged oilwell cement was investigated. The results showed

that the repaired sample recovered piezoresistive behavior and the laterally cracked sample regained

95% of the initial strength.

1. Introduction

Repairing damaged structures after a natural or manmade disaster is an economic way of rehabilitating

the structure rather than reconstructing it. The extend up to which the structural strength could be

regained, after the repair, is a matter of importance. If the structure had self-sensing ability to monitor its

structural health, regaining this sensing ability is another challenge.

2. Objective

Objective of this study was to investigate the effectiveness of using modified ultra-fine cement to repair

damaged oilwell cement in order to regain the strength of structural and piezoresistive properties.

3. Materials and Methodology

Modified class H oilwell cement was used to prepare 2x4” standard cylindrical specimen with a

water:cement ratio 0.4. To determine the strength of the material before damage, these samples were

tested for compressive strength using destructive method with a loading rate of 0.01inch/min. Figure 1

shows the piezoresistive behavior and the strength of the undamaged material after 30 days of curing.

Figure 1: Piezoresistive behavior of initial sample Figure 2: Repaired lab sample

To represent the repaired damaged structure, sample was split into two and was repaired with modified

ultrafine cement, as shown in Figure 2.

0

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Class H cement

Class H cement

Repair material

Sensor

Sensor




II-25

For a better understanding of the repair material itself, 2x4” standard cylindrical ultrafine cement

specimen was made with water: cement ratio 0.6 and its properties were studied. Figure 3 shows its

resistivity behavior from mixing through hardening to curing in the air for 3 hours. The compressive

strength of 21 day old samples and its piezoresistive behavior are shown in Figure 4.

Figure3:Resistivity change of repair material Figure 4:Piezoresistive behavior of repair material

Test results showed that the repairing material itself has approximately equivalent compressive strength

as of class H cement and also it possessed piezoresistive behavior. Then the compressive strength of

repaired sample (shown in Figure 2) was tested and the results are shown in Figure 5 below. The

original sample was made with class H cement and air cured for 30 days before tested. The repaired

sample was allowed to cure in air for 21 days before tested.

Figure 5: Piezoresistive behavior of repaired sample

Above analysis showed that the repaired sample recovered almost 95% of the original strength and it

regained the piezoresistive properties too.

4. Conclusion and Discussion

Using modified ultrafine cement was effective in repairing cracked oil well cement. The results showed

that the repaired material regained 95% of the initial strength and also the piezoresistivity.

5. Acknowledgement

The study was supported by the THC-IT (http://www.egr.uh.edu/hurricane/) with funding from the

industry. Sponsors are not responsible for any of the findings.

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II-26

Effect of Temperature on the Resistivity of

Modified Oilwell Cement mixed with salt water

Pooya Kheiri1, C. Vipulanandan

1 Ph.D., P.E. and D. Richardson



Tel: (713)743-4278: E-mail: [email protected] 2Program Manager – RPSEA, Sugar Land Texas

Abstract：In this study changes in the electrical resistivity of oilwell cement mixed with salt water was

studied at a curing temperature of 170F. Salt water reduced the resistivity. With 6% salt, the resistivity

was reduced by over 80%.

1. Introduction

Traditional cement designs for salt formations have used salt-saturated slurries, assuming they would

bond better with salt formations, resist chemical attack, reduce the tendency for gas migration during

setting and would be less likely to dissolve salt formations. However, at concentrations from about 18%

by weight of water to saturation, salt retards thickening time, reduces compressive strength, increases

thickening time, and promotes fluid loss and free-water content (Ludwig, 1951). Thickening time using

sea water is reduced by about 35.7 percent from that obtained from fresh water, also using sea water

generally increase the early strength development, thereby decreasing the waiting on cement time(Smith,

1975). On the other hand at higher temperatures, hydration starts faster and it leads to accelerated

hardening of cement.

2. Objectives

The objective of this study was to investigate the effect of using salt water to prepare the cement slurry.

Resistivity was used as the monitoring parameter during early curing.

3. Materials and Testing Method

All the materials were mixed at room temperature and cured at 170F. Cement Class H with Different

percentages of salt (NaCl) (0, 2%, 6%) were added to the modified cement with 0.2% conductive

additive. Water-to-cement ratio was 0.5 and Silica fume was added. The two probe calibration factor,

k(R=ρk), was about 50,000 for the specimens without salt contamination and 120,000 for specimens

with salt contamination. These results were for two wires placed at a vertical distance of 1 inch. To

represent the field condition, the specimens were cured in saturated sand, a new method developed

recently.

4. Results

Figure 1 shows initial resistivity at room temperature with different salt percentages. Slurries with

higher percentage of salt had low resistivity, because of the increase in ionic content in the slurry. In this

new way of curing, the weight loss was nearly zero. As shown in Fig 2, the resistivity changed initially

and stabilized after 4 hours. The minimum resistance was observed with both specimens after 50

minutes. After minimum resistance, resistance increased and it was because of hydration and after about



II-27

4-5 hours resistivity decreased. As mentioned before, specimens were cured in saturated sand. It was

observed specimens weight increased with time especially for specimens with high percentage of NaCl.

It could be a reason for the decrease in electrical resistivity after 4-5 hours of mixing.

Figure 3: initial resistivity for slurries with different

salt percentage(mixed at room temperature)

Figure 4: Resistivity change during curing for

slurries with 0 and 6 percent of salt at 170F.

Figure 5: K factor for specimen with 6% NaCl.

Figure 6: weight change during curing.

5. Conclusion

The conclusions are based on the tests performed at 170F with varying amount of salt content. The

conclusions are as follows:

1. Initial resistivity for slurry with 6 percent salt water was about 80% lower than the cement with

water.

2. During the initial curing at 170F resistivity reduced to a minimum within first 50 minutes of

curing.

6. Acknowledgements

This study was supported by Center for Innovative Grouting Materials and Technology (CIGMAT) with

funding from DOE/NETL/RPSEA (Project No. 10121-4501-01).

7. References

Ludwig N. C. (1951). “Effect of Sodium Chloride on Setting Properties of Oil-well Cements.”

Presented at the spring meeting of the mid-Continent District, pp.20-27.

Smith R. C. , Calvert D. G. (1975). “The Use of Sea Water in Well Cementing.” Journal of

Petroleum Technology, pp.759-764.

Lewis W.J., Rang C. L. (1987). “ Salt cements for Improved hydraulic Isolation and Reduce Gas

Channeling.”, SPE 16386.

0

0.2

0.4

0.6

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ial R

esi

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ity(

Oh

m.m

ete

r)

NaCl(%)

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.met

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igh

t ch

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II-28

Effect of Sodium Chloride Contamination on the

Filtration Loss of an Ester based Drilling Fluid R. Prasad

1, C. Vipulanandan

1,Ph.D.,P.E.

1Center for Innovative Grouting Materials and Technology (CIGMAT)



Email:[email protected], [email protected] Phone: (713) 743-4278

Abstract

The effect of Sodium Chloride salt (NaCl) contamination, which would likely occur during a natural

disaster in the offshore drilling site; was studied on the filtration loss of an ester based (60% ester, 40%

water) drilling fluid. The experiments were performed at a constant room temperature. The fluid loss

was studied following API standards by varying the concentration of Salt from 0 to 20%. The presence

of salt brought in considerable increase in the filtration loss.

1. Introduction

Synthetic drilling fluids (SBF) also referred to as pseudo-oil-based inert and non-aqueous drilling fluids

are good alternatives to oil based drilling fluids because they do not have the aromatic compounds and

hence are less toxic. Esters were the first synthetic base used to formulate the drilling fluids. Ester based

drilling fluid system gained its importance in the Oil&Gas industry during the 1990s mainly due to its

high bio-degradability and environmental-friendly characteristics. Due to excessive usage of oil, drilling

is going deeper into the ocean and drilling is done on a larger scale, hence exposing the drilling

operations to likely naturally occurring disastrous conditions. Hence, it is necessary to evaluate the

performance of drilling fluids at different level of contamination conditions. In this study, stability of an

ester based drilling fluid system against salt contamination which could possibly occur during any

disaster like hurricane has been attributed to the fluid loss property measured.

2. Objective

The objective of this study was to determine the effect of Sodium Chloride salt on the filtration loss of

an ester based drilling fluid (60% ester, 40% water) at 100psi pressure and room temperature.


Soybean oil based Fatty Acid Methyl Ester was synthesized in the laboratory using trans-esterification

process at room temperature. The control sample of the ester based drilling fluid had 60% ester and 40%

water with an admixture of 0.2% additive by weight of the ester. Having made a homogeneous mixture

of water and ester by mixing it for 60 seconds, Sodium Chloride salt (NaCl) was added as a % by weight

of water content in to the drilling fluid and was varied from 0 upto 20%. An upper limit of 20% was

used in this experimental program since it is very close to the complete solubility limit of NaCl salt in

water. All samples were prepared and tested at room temperature. Fluid loss (mL) of all the samples

was measured using API Filter Press. All samples were subjected to a constant pressure of 100psi during

the test.

4. Results and Discussions

As shown in Fig.1, the fluid loss of the ester based drilling fluid increases drastically with the presence

of NaCl. It is interesting to note that greater increase was found with lesser percentage contamination of

NaCl i.e. 5% while a considerable reduction was observed when 10% NaCl was added. Also, lesser

change in filter loss was recorded on addition of 10% salt than that of 5%.


II-29

Fig.1. Variation of API filtration loss with time for samples with

constant of ratio ester to water as 60/40

5. Conclusion

It was found that presence of Sodium Chloride salt (NaCl) considerably affected the filtration property

of the ester based drilling fluid. Even though the loss was not of acceptable standards, it reduced

considerably with an increase in the concentration of salt after 5%. Also, upto 5% salt contamination

seems to be detrimental to the filtration properties of Soybean oil Fatty Acid Methyl Ester based drilling

fluid.

6. Acknowledgement

This study was supported by CIGMAT with funding from DOE/NETL/RPSEA (Project 10121-4501-

01).

7. References

1) Carlson, T., and Hemphill.T., “Meeting the Challenges of Deepwater Gulf of Mexico Drilling

With Non-Petroleum Ester-Based Drilling Fluids”, paper SPE 28739 International Petroleum

Conference & Exhibition of Mexico held in Veracruz, Mexico, 10-13 October 1994.

2) Burrows, K., Evans, J., Hall, J., and Kirsner, J., “New Low Viscosity Ester Is Suitable for

Drilling Fluids in Deepwater Applications”, paper SPE/EPA/DOE Exploration and Production

Environmental Conference held in San Antonio, Texas, 26–28 February 2001.

3) Growcock, F.B., and Frederick, T.P, “Operational Limits of Synthetic Drilling Fluids”, paper

SPE 29071 Offshore Technology Conference held in Houston, TX, 2-5 May 1994.

0

50

100

150

200

250

300

0 5 10 15 20 25 30 35

0% NaCl

5% NaCl

10% NaCl

20% NaCl

Filt

rate

loss

(m

L)

Time (min)


II-30

Development of Carbon Nanofiber Aggregate for Concrete Compressive Strain

Monitoring

Rachel N. Howser1, Yuping Liu

1, Y.L. Mo

1 and Gangbing Song

2

1Department of Civil and Environmental Engineering

2Department of Mechanical Engineering

University of Houston, Houston, TX, 77204

Thomas T.C. Hsu Structural Research Laboratory

Abstract

Fiber research in concrete construction is an ongoing field and the use of carbon nanofibers (CNFs) is

critically examined in this study. Short-fiber composites are a class of strain sensor based on the concept

of short electrically conducting fiber pull-out that accompanies slight and reversible crack opening. The

electrical conductivity of the fibers enables the direct current (DC) electrical resistivity of the

composites to change in response to strain damage, allowing sensing. Because of the high cost

associated with CNF, a CNF aggregate (CNFA) is developed. The CNFA is a 16.39 cm3 (1.00 in.

3)

cubic specimen of CNF mortar. It can be embedded in reinforced or prestressed concrete structures and

used to monitor localized damage.

1. Introduction

Because of the past success at the University of Houston demonstrating that self-consolidating carbon

nanofiber concrete (SCCNFC) can be used as a strain sensor (Gao et al. 2009; Howser et al. 2011), a

CNFA was developed to determine localized strain in concrete structures. The development of a CNFA

is significant because it is possible to use the strain sensing capabilities of SCCNFC with a greatly

reduced cost since only the CNFAs placed in the structure would contain CNFs. For the purpose of

compressive strain monitoring, the CNFAs were embedded in concrete cylinders and tested in

compression to determine a relationship between compressive strain and electrical resistance.

2. Development of the Carbon Nanofiber Aggregate

A CNFA is developed with self-sensing capabilities. The CNFA is a 2.54 cm by 2.54 cm by 2.54 cm

(1.00 in. by 1.00 in. by 1.00 in) cube of mortar contain 0.70% CNFs by weight of cement. This size

allowed for both reasonable construction limitations and manageable space in which to place the four

wire meshes needed for the four probe method. The electrical resistance is measured in the CNFAs

through the embedment of four steel meshes and the use of the four-probe method (shown in Fig. 1).

Based on results from the tests completed to determine the optimal CNF dosage, a mix design was

developed to optimize the material and electrical properties. See Table 2 for the CNFA mix design

proportioned by the total weight of the mortar.

The mixing procedure used for the CNFAs is a hybrid of the mixing procedure proposed by the

University of Michigan for a high performance self-consolidating steel fiber reinforced concrete mix

(Liao et al. 2006) and the mixing procedure proposed by the University of Houston for a self-

consolidating CNF concrete (Gao et al. 2009). In this newly proposed hybrid mixing procedure, the

water, high-range water reducer (HRWR), and CNFs were premixed and added to the cement, silica

fume and fine aggregates in several steps to create a homogenous paste. The mixing procedure is

appropriate for small mortar mixes.

3. Carbon Nanofiber Aggregate Compressive Strain Study

The goal of the experiment was to measure how the electrical resistance of an embedded CNFA varies

with strain. The CNFAs were embedded in 7.62 cm (3 in.) by 15.24 cm (6 in.) cylinders. To measure

the electrical resistance, the outer wires of the CNFA were connected in series with a 5.6 kΩ resistor and


II-31

a 10 V power supply. The voltage drops across the inner wires of the CNFA and resistor were measured

using the data acquisition system dSpace. As there was an impedance problem within the data

acquisition system, differential amplifiers were placed between each component of the circuit and the

data acquisition system. Here we discuss two groups of cylinders. Group 1 contains 12 cylinders using

monotonic loading, Group 2 contain 3 cylinders using cyclic loading.

Table 2 CNFA Mix Design

Material

Percentage of

Total

Mortar Weight

Fine

Aggregate

52.9%

Cement 28.6%

Water 12.14%

Silica Fume 4.29%

HRWR 1.957%

CNFs 0.200%

Fig. 1 Four Probe Method

The experimental results for Group 1 showed that when each cylinder began loading as the electrical

resistance variation (ERV) increases from 0 simultaneously with the stress and strain. The maximum

ERV occurs near a strain of 0.001 for each case. From the voltage variation (VV) curves, failure is

clearly shown by a sudden drastic change in the negative direction. After introducing a calibration factor

to reduce the variation in the tested results, Equation 1 was developed to describe the relationship

between calibrated ERV and strain (shown in Fig. 2).

11259.7393

C

ERVc Equation 1

where:

ERVc: Calibrated ERV.

Fig. 2 Strain versus Calibrated ERV for Group 1

Group 2 contained 3 cylinders using displacement-control cyclic loading. A base displacement of 0.0381

mm (0.0015 in.) was chosen. Two cycles were applied at n times the base displacement where n=1, 2, 3,

etc. until failure. The experimental results for Cylinder A are shown in Fig. 3, the other two cylinders

exhibited similar behavior. Some simple modifications were made to the model found for Group 1 in an

attempt to predict the cyclic behavior of embedded CNFAs. The model is shown graphically in Fig. 4

and Equations 2-5. Cylinder A was modeled using the proposed equations; the validation shows the

calibrated and modeled EVR versus time and strain roughly agree.

0

0.05

0.1

0.15

0.2

0.25

0 0.0005 0.001 0.0015 0.002 0.0025

Ca

lib

rate

d E

RV

Strain

Model

Model + StdDev

Model - StdDev


II-32

Fig. 4 Cyclic Strain versus Calibrated ERV Model

For curve A-C-B, it follows Equation 1

For curve C-D, it follows:

tttu

CERVR 11259.7

3933

2 Eq.2

uu RC

ERV 11259.73933

2 Eq.3

For curve D-E, it follows:

tttr

CERVR 11259.7

393 Eq.4

rr RC

ERV 11259.7393

Eq.5 Fig. 3 Cylinder A Stress, Strain, and ERV versus Time

4. Summary

A carbon nanofiber aggregate (CNFA) was developed with self-sensing capabilities. Two groups of

cylinders with CNFAs embedded were tested in compression monotonically and cyclically. A

qualitative assessment of the electrical data from a CNFA embedded in a cylinder can show when

loading began on the cylinder, a strain of approximately 0.001, and failure. A calibration factor was

applied to the ERV value to obtain a reasonable coefficient of variation and two models were developed

to estimate the monotonic and cyclic ERV versus strain relationship.

5. Acknowledgement

The study was funded by the National Science Foundation and the American Society of Civil Engineers,

and the chemical admixtures for this study were donated by Master Builders Inc. (USA).

6. References

1. Gao, D., Sturm, M., and Mo, Y. L. (2009). “Electrical resistance of carbon-nanofiber concrete.”

Smart Materials and Structures, 18(9).

2. Howser, R. N., Dhonde, H. B., and Mo, Y. L. (2011). “Self-sensing of carbon nanofiber

concrete columns subjected to reversed cyclic loading.” Smart Materials and Structures, 20(8), 085031.

3. Liao, W. C., Chao, S. H., Park, S.-Y., and Naaman, A. E. (2006). Self-Consolidating High

Performance Fiber Reinforced Concrete (SCHPFRC) – Preliminary Investigation. NSF Program: NEES

Research, 76.


II-33

Monitoring Crack Growth in Layered Polymer Composite Beams using Digital

Image Correlation (DIC) System Y. J. Ahossin Guezo and C. Vipulanandan

Texas Hurricane Center for Innovative Technology (THC-IT) Department of Civil and

Environmental Engineering, University of Houston, Houston, Texas 77204-4003

Email: [email protected]

Abstract

In this study, deformation field of notched multilayered polymer composite beams were investigated

using a Digital Image Correlation (DIC) system. The notched beams were made of four layers of

different polymers: three layers of different types of composites polypropylene and one layer of epoxy.

The multilayered polymer composites are used as subsea pipe thermal insulation. The Crack Mouth

Opening Displacement (CMOD) and Crack Tip Opening Displacement (CTOD) were monitored using

the DIC system with the delamination of layers. The CMOD and CTOD were measured to an accuracy

of 0.001 mm.

1. Introduction

Fractures induce catastrophic failure of materials and their prediction is done using fracture mechanic

concept. Fracture mechanics is a relatively new field of mechanics and it is concerned with the study of

the propagation of cracks in materials. Its foundation was established by Griffith (Griffith, 1921) based

on the work of Inglis’ 1913 work on infinite plate loading by uniaxial stress. Griffith worked on brittle

material (glass), and consequently established the Linear Elastic Fracture Mechanic which was extend to

Elastic-Plastic Fracture Mechanics, by the introduction of J-integral for nonlinear elastic and ductile

materials, with the work of Rice (Rice, 1968) in consideration to the work of Cherepanov (1960). The

application of fracture mechanics resides in the detection of small cracks present during the fabrication

of part or crack developed in service and their potential to grow into unstable cracks leading to

catastrophic failure. The yield strength of the material, the working temperature and fatigue also play an

important role in fracture mechanic failure. The latter make the material brittle or reduce it yield stress

respectively. The interest of this study is to investigate crack evolution through the different layers of the

composite beams in consideration of the initial crack location.

2. Experimental tests

The composite beams were approximately

362 mm (14.25 in) long, 70 mm (2.76 in)

high in average, and 38 mm (1.5 in) width.

The four point bending was configured as

shown in Fig. 1 (a). The test setup with the

DIC system is shown in Fig. 1 (b). The

accuracy of the DIC in comparison with the

strain gage reading was first checked for

reliability.

(a) (b)

Figure1. Bending tests: (a) Sketch of the four points bending loading and (b) DIC setup picture.


The deformation fields of the notched composite beams were monitored using the digital image

correlation system. Two types of test results are presented: monotonic quasi static loading until failure,

shown in Fig. 2 (a), and monotonic cyclic loading, shown in Fig. 2 (b). In the case of specimen of

monotonic loading, the notched was stopped in the brittle layer. The CMOD evolution up to the

PP

304.8 mm (12'')

101.6 mm (4'')

2

3

P P

1

4


http://en.wikipedia.org/wiki/Mechanics


II-34

specimen failure was monitored as shown in Fig. 3 (a). As shown in Fig. 2 (a), the crack evolved

through layer 3 followed by the complete delamination of the layer 3 and 2 and the complete fracture of

layer 2 following the path of the maximum stresses under the loading points.

(a) (b)

Figure 2. Lateral strain field distribution: (a) Monotonic loading, (b) Cyclic loading

(a) (b)

Figure 3. CMOD and CTOD recorded using DIC system: (a) monotonic and (b) cyclic loading.

Note: Delam. = delamination

The bending strain field, in the case of cyclic loading, is shown in Fig. 2 (b). The maximum strain zone

is in red around the crack tip. The CTOD evolution with applied load is also plotted in Fig. 3 (b). These

fracture parameters, strain field, CTOD and CMOD were extracted from the deformation field on the

notched composite beams captured by the Digital Image Correlation system.

4. Conclusion

The strain field, the CTOD and the CMOD of notched layered composite beams, in four points bending,

were monitored using a Digital Image Correlation system. The advantage of the DIC system was that a

complete deformation field, displacement and strain, can be obtained, specially the crack front strain

distribution.

5. References

Griffith, A. (1921) “The phenomena of rupture and flow in solids.” Philosophical transactions of the

royal society. 221, 163-198.

Rice, J. (1968) “A path independent integral and the approximate analysis of strain concentration by

notches and cracks.” Journal of Applied Mechanics, 35, 379-386.

0

1500

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0 5 10 15 20 25

Forc

e (N

)

CMOD (mm)

Delam.

Start

Delam.

End

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6000

7500

0.00 0.50 1.00 1.50

Forc

e (N

)

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Notch


II-35

Phase Behavior of Mixtures of Polymer Functionalized Nanoparticles

And a Polymer Matrix Katrina Irene Mongcopa and Ramanan Krishnamoorti

Department of Materials Engineering

Department of Chemical and Biomolecular Engineering

University of Houston, Houston, TX, 77204

Tel: (713)743-4314 Email Address: [email protected]

Abstract

In this study, the thermodynamic interactions of polystyrene (PS) grafted onto spherical silica particles

(15 nm in diameter) with poly(vinyl methyl ether) (PVME) are investigated. The characteristics of the

PS hybrid nanoparticles as well as its blending behavior with the PVME matrix are analyzed using light

and x-ray scattering techniques.

1. Introduction

Organic-inorganic hybrid materials are known to exhibit polymeric features that are significantly

enhanced by the inclusion of small and hard inorganic particles in the melt matrix. The favorable

interactions between these two entities contribute to improved thermal, mechanical and electronic

properties that are otherwise compromised in the pure materials. Previous efforts in dispersing

nanoparticles, whether in solution or with another polymer, have shown that such phenomenon is largely

driven by entropic and enthalpic contributions to the total free energy. Favorable particle–polymer

interactions in which the Flory interaction parameter of the melt matrix with the grafted polymer brush

is negative (χ < 0) lead to dispersion; while strong van der Waals attractions between the particles result

in aggregation.

2. Objective

The objective of this study is to understand the interplay among the tunable characteristics of the

nanoparticles on the phase behavior and concentration fluctuations for strongly interacting polymer

blends of PS-silica hybrids and PVME using Dynamic Light Scattering (DLS) and Small Angle X-ray

Scattering (SAXS).

3. Analyses

PS-silica hybrid nanoparticles with a tethered brush molecular weight of 16,000 g/mol were synthesized

and characterized using thermogravimetric analysis (TGA), gel permeation chromatography (GPC) and

DLS. These nanoparticles were solution mixed with PVME having a molecular weight of 18,000 g/mol

to yield a polymer blend of the desired PS:PVME weight composition. The inter-particle distance d

derived from the scattering vector q for the pure hybrid and PS-PVME blends was obtained using

SAXS.

4. Discussion

The design and synthesis of these PS hybrid nanoparticles involve the atom transfer radical

polymerization (ATRP) technique which allows control over the grafting density, composition and

molecular weight of the tethered polymer. Results from TGA and GPC reveal a polymer grafting density

and grafting efficiency of 0.5 chain/nm2 and 45%, respectively. In addition, a monodisperse PS brush

with a weight average molecular weight of 16,000 g/mol and polydispersity index of 1.16 was obtained.



II-36

The size of the hybrid nanoparticles dispersed in toluene was found to be 48.48 (±0.10) nm, as indicated

by DLS results. The change in the inter-particle distance for the PS16k/PVME18k blend with increasing

temperature was monitored using SAXS. It was found that at a critical composition of 20/80

(PS16k/PVME18k), q shifts to higher values, indicating a change to smaller inter-particle distance as the

lower critical solution temperature (LCST) phase transition is reached. Such behavior signifies swelling

of tethered PS brush by PVME which facilitates the dispersion of the PS-silica hybrid within the PVME

matrix.

Figure 1. SAXS data for a 20/80 PS16k-PVME18k blend at different temperatures.

5. Conclusions

PS-hybrid nanoparticles can be prepared by ATRP to produce materials with controlled molecular

weight, composition and grafting density. The LCST phase transition for a 20/80 PS16k/PVME18k

blend composition is observed at higher temperatures.

6. Acknowledgement

We would like to thank Nissan Chemicals for the silica particles and ExxonMobil Chemical Company

for funding. We also acknowledge NSF (DMR 1040446 for support of the SAXS/WAXS

instrumentation through the MRI program and funding provided by DOE/NETL/RPSEA (Project

10121-4501-01).

7. References

1. Borukhov and Leibler, Macromolecules, 2002, 35, 5171–5182.

2. Gharachorlou and Goharpey, Macromolecules, 2008, 41 (9), 3276–3283.

0.01 0.1

0.01

0.1

1

I(q

)

q(A-1)

roomtemp

50C

65C

70C

75C

80C

90C

100C

105C

115C

annealed70C


II-37

pH-responsive behavior of aqueous CTAB/NaSal solutions

Chinedu Umeasiegbu1, Ramanan Krishnamoorti

1,2, and Vemuri Balakotaiah

1,2

Department of Chemical and Biomolecular Engineering1 and Petroleum Engineering Program

2,

University of Houston, Houston, TX 77204

Abstract

In this study, we investigate the pH-responsive behavior of an aqueous solution of

cetyltrimethylammonium bromide (CTAB) in the presence of sodium salicylate (NaSal). The fluid can

be switched between gel-like and fluid-like within a narrow pH range.

1. Introduction

About 60% of the world’s remaining oil reserves are contained in carbonate reservoirs which are often

heterogeneous with wide permeability variations. In the matrix acidization of carbonate reservoirs,

injected acid preferentially flows into high permeability zones leaving lower permeability zones

unstimulated. Thus diversion techniques have to be employed to ensure total zonal coverage of the

formation and hence effective stimulation. Certain self-assembly systems such as the CTAB/NaSal

system exhibit pH response becoming viscoelastic upon an increase in pH due to a transformation from

spherical to wormlike micelles and this can be utilized in ensuring effective stimulation in

heterogeneous carbonate reservoirs.

2. Objective

The objective of this study is to fundamentally understand the change in rheological behavior that results

with changing pH.

3. Analyses

The bubble recoil test which involves swirling solution containing vials and observing the movement of

small bubbles trapped in it was used to determine the pH at which the aqueous CTAB/NaSal solutions

lose their viscoelasticity. Fluorescent polystyrene particles dispersed in aqueous solutions of CTAB and

NaSal were imaged on an inverted microscope. To extract the rheology of the solution from the time-

dependent microscopy images of the polystyrene particles, we implemented a particle tracking algorithm

to obtain the time evolution of the mean square displacement (MSD) from which we obtained the

storage and loss moduli using the numerical method of Mason and Weitz.

4. Discussion

Dynamic light scattering (DLS) measurements were done on 2.5mM CTAB/2.5mM NaSal (Fig. 1). It

can be seen that the relaxation time of the micelles decreases with decrease in pH indicating a transition

from wormlike to spherical micelles. The addition of NaCl does not change the transition pH indicating

that the pH-responsive behavior is primarily due to the presence of Sal-. The pH at which different

concentrations of aqueous CTAB/NaSal solutions lose their viscoelasticity (Fig. 1) was obtained from

the simple bubble recoil test.


II-38

Figure 1. (Left) Relaxation time vs pH for an aqueous solution of 2.5mM CTAB/2.5mM NaCl. (Right)

Phase diagram for CTAB-NaSal solutions showing transition pH

5. Conclusion

It was revealed that the transition pH of these solutions and the associated change in rheology and

viscosity of the system upon transition was dependent on the NaSal to CTAB ratio (Cs/Cd) and on the

concentration of CTAB (Cd)。

6. Acknowledgement

We acknowledge funding provided by DOE/NETL/RPSEA (Project 10121-4501-01). Sponsors are not

responsible for any of the findings in this study.

7. References

Chang, F.; Qu, Q.; Frenier, W. SPE 65033 2001

Aswal, V. K.; Goyal, P. S.; Thiyagarajan P. J. Phys. Chem. B. 1998, 102, 2469-2473

Rodrigues, R. K.; Silva, M. A.; Sabadini, E. Langmuir 2008, 24, 13875-13879

Mason, T. G.; Weitz, D. A. Phys. Rev. Lett. 1995, 74 1250-1253

effect of oil contamination and temperature on the...

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