Surfactant-Based Mobility Control - American Chemical Society

Chapter 8

Downloaded by CALIFORNIA INST OF TECHNOLOGY on November 22, 2017 | http://pubs.acs.org Publication Date: July 20, 1988 | doi: 10.1021/bk-1988-0373.ch008

Surfactants for Carbon Dioxide Foam Flooding Effects of Surfactant Chemical Structure on One-Atmosphere Foaming Properties 1

1

1

2

John K. Borchardt , D. B. Bright , M . K. Dickson , and S. L. Wellington 1

Westhollow Research Center, Shell Development Company, P.O. Box 1380, Houston, TX 77251-1380 Bellaire Research Center, Shell Development Company, P.O. Box 481, Houston, TX 77001 2

A one atmosphere foam test has been designed to permit the study of large numbers of surfactants and the identification of promising candidates for evaluation under reservoir conditions. The inclusion of an o i l phase in these experiments is a key feature which allows the effect of o i l composition on surfactant foaming to be studied. Classes of surfactants studied included alcohol ethoxylates, alcohol ethoxysulfates, alcohol ethoxyethylsulfonates and alcohol ethoxyglycerylsulfonates. The ability to test large numbers of surfactants permits the relationship of surfactant chemical structure and physical properties to foaming properties to be studied. Surfactants which performed well in the 1 atmosphere foaming experiment were also good foaming agents in sight cell and core flood experiments(1,2) performed in the presence of CO and reservoir fluids under realistic reservoir temperature and pressure conditions. Therefore, i t appears that the one atmosphere foaming experiment is a useful screening test. 2

Core floods and high pressure sight c e l l experiments are unsuitable for screening large numbers of surfactants as mobility control agents because of the long duration of the experiments. The high cost of the required experiment prevents the performance of a large number of tests. Care must be taken to achieve reproducible foam generation i n both core floods and sight c e l l foaming experiments. For example, i n sight c e l l studies the rate of generation, "foam" c e l l geometry, and s t a b i l i t y of s u p e r c r i t i c a l C0 "foams" can vary from one sight c e l l to another probably due to v a r i a t i o n s i n the nominally i d e n t i c a l sintered glass tubes used to generate the foam. Therefore, comparison of s u p e r c r i t i c a l C0 "foaming" properties of various surfactants may best be performed i n the same sight c e l l 2

2

c

0097-6156/88/0373-0163$06.00/0 1988 American Chemical Society

Smith; Surfactant-Based Mobility Control ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

SURFACTANT-BASED MOBILITY CONTROL


164

apparatus. This prevents the simultaneous performance of experiments . The u n s u i t a b i l i t y of core floods and sight c e l l experiments for screening large numbers of surfactants led to the consideration of a one atmosphere foaming test. The advantages of a one atmosphere foaming experiment are that a reproducible experiment can be designed, the test design allows the evaluation of a large number of surfactants i n a r e l a t i v e l y short time, and the evaluation can be performed i n the presence of reservoir brine and o i l at format i o n temperature. The c a p a b i l i t y to determine comparative foaming properties i n the presence of an o i l phase and the e f f e c t of o i l phase composition on foaming are p a r t i c u l a r l y important features of the one atmosphere experiment. Previous one atmosphere test designs did not allow for the study of the e f f e c t of o i l phase composition. However, there are strong p o t e n t i a l objections to the use of a one atmosphere foaming experiment to evaluate surfactants. These objections must be considered to determine the relevance of one atmosphere foaming experiments to surfactant performance i n a reservoir. Bikerman has noted that while shaking i s the simplest method of producing foam, "the height and volume of the foam obtained depend on the d e t a i l s of the shaking procedure...and thus cannot be used to characterize the foaminess of a l i q u i d i n a (reasonably) absolute manner...the foam heights reproduced are s p e c i f i c for the test procedure selected and have no general validity."(3) The purpose of the one atmosphere experiment described herein i s to determine the r e l a t i v e not the absolute foaming properties of surfactants and to determine the best candidates for evaluation under r e a l i s t i c reservoir conditions. Therefore, the dependence of foam volumes on the experiment design are not of concern as long as the one atmosphere experiments are performed i n a reproducible manner and the test design i s such as to d i s t i n g u i s h between poor, mediocre, and good candidates for testing under reservoir conditions . C e l l size and uniformity are also important variables when studying foams. However, space l i m i t a t i o n s preclude discussions of these variables herein. Other surfactant properties c r i t i c a l to the success of an EOR process are surfactant adsorption and thermal s t a b i l i t y . These questions, under study i n our laboratory, are not considered i n the short-term one atmosphere foam test experiment and therefore w i l l not be discussed herein. 3

Experimental Section Surfactants Studied Ethoxylated surfactants were chosen for study based on predicted foaming properties, thermal and chemical s t a b i l i t y , and adsorption c h a r a c t e r i s t i c s . Only foaming properties are discussed herein. Our naming system for the alcohol based surfactants i s : 1.

class designation using a 2-4 l e t t e r acronym AE — alcohol ethoxylate AES — alcohol ethoxysulfate


8. BORCHARDTETAL.


2. 3.

165

Surfactantsfor CO Foam Flooding 2

AESo - alcohol ethoxyethyl sulfonate AEGS = alcohol ethoxyglyceryl sulfonate carbon number range i n the hydrophobe (R) average number of ethylene oxide units

AE and AES samples were commercial or developmental ENORDET surfactants from Shell Chemical Company except f o r AES 810-2.6 supp l i e d by GAF Corporation. AESo and AEGS surfactants were experimental research samples synthesized i n our laboratories or were supplied by Koninlijke/Shell Laboratorium Amsterdam with the exception of AESo 911-2.5, 911-3.25, 911-4, and 1215-12 obtained from Diamond Shamrock Corporation. Experimental Section 1 Atmosphere Foaming Test(4) This s t a t i c test involves the generation of foams i n the presence or absence of hydrocarbon phases at temperatures from 24°C (77°F) to 90°C (194°F). Sometimes warming was required to prepare the 0.5% surfactant solutions i n brine. The surfactant solution (lOcc) was placed i n a clean tared 25cc graduated cylinder. The hydrocarbon phase: decane, decane/toluene (1:1 by volume), stock tank o i l , or s u p e r c r i t i c a l C0 -extracted stock tank o i l (3.0cc) was then added. In tests using t y p i c a l west Texas stock tank o i l , carbon dioxide was then passed over the surface of the l i q u i d to remove most of the a i r from the headspace. Samples were shaken after temperature e q u i l i b r a t i o n , allowed to stand f o r 24 hours, and shaken again. Foam volume was then determined at set times. This method was chosen over continuous monitoring i n order to perform more experiments simultaneously. Detailed k i n e t i c s of foam decay were not required to determine r e l a t i v e foaming properties of surfactants (see above). The one atmosphere foam test was found to be quite reproduci b l e when performed by a single operator. Average deviations i n foam volumes were 0.3-0.7cc. This was more than s u f f i c i e n t to d i s t i n g u i s h excellent foaming agents from good ones and good foaming agents from poor ones. However, rank ordering of surfactant foam volumes within these categories ( p a r t i c u l a r l y the poor foaming agents) was occasionally complicated by experimental errors i n foam volumes. The following synthetic brines were used i n the f i r s t series of tests: 2

2

%w Brine Designation 0.5X 1.0X 1.5X 2.OX

NaCl

CaCl

5.19 10.38 15.57 20.76

0.38 0.76 1.14 1.52

2

[Ca+ ] (ppm) 1372 2745 4118 5490


166


Preparation of the synthetic west Texas brine i s described i n reference 4. This brine had the following composition p r i o r to filtration: NaCl NaHC0 Na S0 CaCl MgCl

40.38g/1000cc 2.00g/1000cc 3.06g/1000cc 7.02g/1000cc 2.25g/1000cc

3

2

4

2


2

The west Texas stock tank o i l and stock tank o i l extracted with C0 for eight hours at 40°C and a pressure of approximately 2200 psig were used i n other experiments. Composi tions of these o i l s are given below: 2

Analysis

Stock Tank O i l

Stock Tank O i l

a) Median Carbon Number

16

% asphaltenes % sulfur 25°C Surface Tension (dynes/cm)

0.78

1.52

1.95 26.7

2.67 29.6

25°C Density (g/cc)

0.8588

Total Acid and Base Number

0.33

a) Determined technique.

using

a

high

26

pressure

0.9140 0.85

liquid

chromatographic

High Pressure Sight C e l l Studies A high pressure windowed test c e l l was charged with a 0.5% solution of surfactant i n 1.0X brine. The c e l l was heated to 75°C and pressurized with C0 to a pressure of 2500 psig (1.7237 Χ 10 Pa). A 1:1 volume r a t i o of l i q u i d and C0 was used. The charged c e l l was then agitated u n t i l i t s contents became thoroughly mixed. As soon as the f l u i d s became s t a t i c (ca 1 min), the foam height was measured. A second measurement was made 30 minutes l a t e r . 7

2

2

Results E f f e c t of Surfactant Structure on Foam Volume At 75°C (167°F), a representative U.S. Gulf Coast formation tem perature, AES, AEGS, and AESo surfactant classes produced f a i r l y stable foams i n short-term tests (see Table I ) . Examination of these data indicated that the AEGS surfactants generally gave the


8. BORCHARDTETAL.

167

Surfactantsfor C0 Foam Flooding 2


greatest r e l a t i v e foam s t a b i l i t y at higher s a l i n i t y . Representative data plotted i n Figure 1 indicated that at 75°C i n the presence of decane, AEGS surfactants produced more stable foams than AESo, AES, and AE surfactants having very similar hydrophobes and comparable EO contents. E f f e c t of Number of EO Groups Examination of the data summarized i n Table I indicated that, at a constant number of carbon atoms i n the hydrophobe, foam s t a b i l i t y generally increased as the number of ethylene oxide groups was i n creased. The e f f e c t of a change i n EO l e v e l on foam volume i n the presence of a hydrocarbon phase was generally greater at lower EO l e v e l s (Figure 2^. For some o i l s such as west Texas stock tank o i l , the foam volume reached a maximum at ca 20-30 moles EO per mole AE and then decreased. The e f f e c t of EO l e v e l on the 75°C 10 minute foam volume ( i n 1.0X brine i n the presence of decane) produced by AEGS and AESo surfactants having the same hydrophobe i s shown i n Figure 1. The AEGS foam volume increased more rapidly with increased EO l e v e l than d i d foam volumes of AESo surfactants i n the absence of an o i l phase. The value of the 1.0X:1.5X brine foam volume r a t i o at 75°C may be taken as a measure of the s e n s i t i v i t y of surfactant foaming properties to aqueous phase s a l i n i t y . Values of this r a t i o determined at 75°C i n the presence of decane are summarized below:

a) b)

Surfactant

10 min Foam Volume Ratio 1.0X:1.5X B r i n e

AES 911-2.5 AES 911-5 AES 911-8

1.17 0.80 4.0

AES 1215-3 AES 1215-6

0 0.40

AESo AESo AESo AESo

1215-3 1215-6 1215-12 1215-16

0.8 2.27 5.71

AEGS AEGS AEGS AEGS

1215-3 1215-7 1215-12 1215-18

1.50 1.75 2.25 2.50

a ;

b)

AESo and AEGS surfactants were experimental research samples. Ratio - 2.3/0


Smith; Surfactant-Based Mobility Control ACS Symposium Series; American Chemical Society: Washington, DC, 1988. -11.4 6.6 2.0 5.7 3.1

AES 1213-6.5A

AES 1213-12A

AES 1215-3S

AES 1215-6S

AES 810-2.6A

3.1

AES 911-8S

AES 911-5S

AES 911-2.5S

19.9

0.5

AE 1215-18

Alcohol Ethoxysulfates

0 2.8

AE 1215-12

.

No O i l

AE 1215-7

Alcohol Ethoxylates

Surfactant 7

4.0

6.4

3.0

4.0

5.0

~

3.6

6.0

3.3

0.2

0

D

0.5X Brine

0

1.0

1.9

0

4.0

1.0

—

8.0

3.0

0

0

D/T

Table I.

8.8

6.0

13.0

4.8

10.2

0.4

5.0

21.3

0.8

0

0

No O i l

3.0

2.0

0

6.0

4.0

7.2

4.0

7.0

0.8

0

0

D 0

1.0X Brine

2.0

0

0

0.1

0

—

1.2

1.0

0

0

D^T

6.2

18.4

12.2

9.8

20.8

1.6

7.3

21.7

0.7

0

0

No Oil

3.0

5.0

0

6.0

6.0

1.8

5.0

6.0

2.4

0

0

D 0

1.5X Brine

10 Minute Foam Volume (cc)

ο ο 75 (167 F) One Atmosphere Foaming Studies

0

0

0

0

0

0.3

1.0

0

0

D/T


18.8

19.9

5.7

3.6

20.4

15.9

21.8

0

0

0

No Oil

1.0

1.0

0

2.0

1.0

3.0

4.0

0

0

D 0

2.OX Brine

0

0

0

0

0

0

0

0

0

0

D/T

8. BORCHARDTETAL.


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Ν

Ν

Η


172



This foam volume r a t i o generally increased with increasing surfactant EO content, for example AEGS 1215-3 < AEGS 1215-7 < AEGS 1215-12 < AEGS 1215-18. At 25°C, this r a t i o for AES surfactants was less sensitive to s a l i n i t y and EO content than at 75°C. The l i m i t e d hydrolytic s t a b i l i t y of AES surfactants(4-8) renders the relevance of the short-term 75°C data to long-term low pH f i e l d applications questionable. Cloud point data indicated that the 75°C t e s t temperature was above the cloud point of these AE surfactants (which ranged from 49-66°C i n 10% NaCl brine and decreased with increasing aqueous phase s a l i n i t y ) . Temperature Effects on Foaming Results summarized i n Table I indicated that foam s t a b i l i t y genera l l y decreased with increasing aqueous phase s a l i n i t y . The e f f e c t of surfactant functional group on s a l t s e n s i t i v i t y may be considered by comparing the behavior of AE, AESo, and AEGS surfactants. Surfactants being compared have s i m i l a r hydrophobes and approximately the same number of EO groups i n the hydrophile. (Differences i n the method of synthesis of some of these surfactants can r e s u l t i n d i f f e r e n t d i s t r i b u t i o n of the number of hydrophobe carbon atoms and of the EO content about the average values. Also the i d e n t i t y and concentration of impurities may vary. These changes could e f f e c t the observed results.) The r a t i o of foam volume i n 2.OX brine to that i n 0.5X brine at 75°C (Table II) served as a measure of surfactant s a l t s e n s i t i v i t y . This r a t i o declined i n the order: AEGS 1215-12 > AESo 1215-12 ~ AE 1215-12. This decline indicates that AEGS 1215-12 foam s t a b i l i t y was less sensitive to the presence of s a l t s i n the aqueous phase than the other classes of surfactants studied. E f f e c t of O i l on Foaming - Refined Hydrocarbons Unlike previous one atmosphere foam test designs, the present test permits the e f f e c t of the o i l phase on surfactant foaming propert i e s to be determined. Refined hydrocarbons were used as model o i l phases. Results summarized i n Tables I and Figure 3 indicated that the presence of hydrocarbons decreased the foam s t a b i l i t y . Examination of Table I indicated that the presence of a hydrocarbon substantially reduced the 75°C foam volumes produced by AES and AESo surfactants. At higher EO l e v e l s , the foam volume produced by AEGS and AESo surfactants were less adversely affected by the presence of an o i l phase than were other surfactants studied (Table I. Figure 1). This behavior was l i k e l y due to the formation of an oil/water emulsion which s t a b i l i z e d the f l u i d films between gas bubbles. Although foam volumes were smaller, at 75°C i n three d i f f e r e n t brines, the s e n s i t i v i t y of AE and AES surfactants to the presence of decane decreased with increasing surfactant ethylene oxide content. In contrast, the presence of decane generally had little detrimental e f f e c t on the AEGS 10-minute foam volume under these test conditions. However, the AEGS surfactants d i d exhibit s i g n i f i c a n t l y reduced foam volumes i n the presence of a 1:1 blend of decane and toluene.


8. BORCHARDTETAL.


Table I I .

173

Surfactantsfor C0 Foam Flooding 2

Effect of an O i l Phase and Aqueous Phase S a l i n i t y on Surfactant Foaming Properties

AES 911-2.5 AES 911-5 AES 911-8

Foam Volume Ratio Decane/No O i l 0.5X 1.0X 1..5X 2.OX 0 .30 0..33 0..28 0.18 1,.16 0..80 0..68 0.19 ND 18,.0 ND 1..1

AES 1213-6.5A AES 1213-12A

0,.44 0 .61

0..39 1..25

0..29 0..61

0.05 0.56

AES 1215-3 AES 1215-6

1,.50 1,.12

0 0..33

0 0..27

0 0.05

AESo 911-2.5 AESo 911-3.25 AESo 911-4

0 .84 0,.27 0 .44

0..32 0..29 1..21

0..10 0..47 1..30

0.04 0.01 0.01

AESo AESo AESo AESo AESo

0 .40 0 .48 0 .92 0 .93 8 .0

0 0,.20 0,.62 0,.45 2,.11

0 0 0,.06 0,.15 0,.44

0 0 0 0.13 0.01

4,.75

2.60

0,.32 1,.33 1,.08 0,.87

0 0.42 0.65 0.50

1215-1 1215-3 1215-6 1215-12 1215-16

AEGS 911-8 AEGS AEGS AEGS AEGS

1215-3 1215-7 1215-12 1215-18

18 .3 2 .0 0 .33 2 .50 5 .42

11,.5 0,.29 7,.0 2,.50 2,.38

N O T E : N D = not determined. AESo and AEGS surfactants were experimental research samples synthesized for this study.




Figure 3. Effect of o i l phase and number of ethoxy groups on foam volume produced by sulfonate surfactants.


8. BORCHARDTETAL.

Surfactants for CO Foam Flooding 2

175


Increasing the aqueous phase s a l i n i t y appeared to increase foam s e n s i t i v i t y to the presence of a hydrocarbon phase. This behavior may be due to increased surfactant p a r t i t i o n i n g into the o i l phase. This can be quantified by determining the r a t i o of foam volume i n the presence of decane to that i n the absence of an added hydrocarbon (Table I I . Figure 3). With few exceptions, t h i s r a t i o decreased with increasing aqueous phase s a l i n i t y . The values of t h i s r a t i o f o r AEGS surfactants declined less with increasing aqueous phase s a l i n i t y than f o r other surfactants. E f f e c t of O i l Composition The r a t i o of foam volume i n the presence of a 1:1 (by volume) blend of decane and toluene vs that i n the presence of decane alone i s a measure of the s e n s i t i v i t y of surfactant foaming properties to the aromatic content of the o i l phase. Since the values of t h i s r a t i o were less than unity, aromatic species as represented by toluene had a more negative e f f e c t on foam s t a b i l i t y than a l i p h a t i c hydrocarbons such as decane. Toluene s e n s i t i v i t y appeared to increase with increasing aqueous phase s a l i n i t y and to decrease with increasing surfactant EO content. Again, this may r e f l e c t surfactant p a r t i t i o n i n g behavior. AEGS, AESo, AES, and AE surfactants did not d i f f e r greatly i n toluene s e n s i t i v i t y i n 0.5X brine. When the aqueous phase s a l i n i t y was increased, AEGS foam volumes were the least affected by the presence of toluene i n the hydrocarbon phase. For most of the AES surfactants studied, the r a t i o of foam volume i n the presence of added decane to that i n i t s absence was r e l a t i v e l y constant over the 0.5X-1.5X s a l i n i t y range but decreased s i g n i f i c a n t l y when the solvent was 2.OX brine. Limited data on two compounds (the sodium and ammonium AES 911-2.5 s a l t s ) i n 1.0X and 1.5X brines at 75°C indicated no obvious dependence of decane foaming s e n s i t i v i t y to the i d e n t i t y of the AES counterion. E f f e c t of Stock Tank O i l Procedures of these 40°C (104°F) experiments are described i n the Experimental Section. Tests were performed at a representative west Texas formation temperature using a t y p i c a l west Texas stock tank o i l and a synthetic brine having a composition t y p i c a l of west Texas i n j e c t i o n waters. Results are summarized i n Table I I I . The r a t i o of foam volume after 30 minutes at 40°C to that a f t e r 1 minute was used as an indication of foam s t a b i l i t y . The surfactants which produced the greatest i n i t i a l (1.0 minute) foam volumes also exhibited the greatest foam s t a b i l i t y over the t h i r t y minute test period. Because test temperature and s a l i n i t y were d i f f e r e n t than used i n e a r l i e r experiments, results i n the presence of west Texas stock tank o i l cannot be compared to results described above. However, trends i n foam s t a b i l i t y were consistent with those described above. Average s t a b i l i t y of the foams produced by the AEGS and AES surfactant classes was greater than that of the AE foams. The 30-minute foam volume i n the presence of stock tank o i l vs EO content of a series of C alcohol ethoxylates was p l o t t e d i n Figure 2. Foam volume was "a maximum at approximately 30 moles 1 2

1 5



N O T E : STO = stock tank oil. See experimental section for test procedures. S = sodium couterion. AESo and AEGS surfactants were experimental research samples synthesized for this study.

--

0.9 0.7 0.9 0.9 0.7 0.9 0.3 0.9 0.9 0.7 0.8

20.7 13.4 20.7 20.8 12.5

19.8 3.8 20.0 20.2 10.1 11.9

AES 911-2.5S AES 1215-3S AESo 911-2.5S AEGS 911-8 AEGS 1215-12 AEGS 1215-18

0.4 0.6 0.4 0.3 0.1 0.4 0.7 0.8 0.7 0.7

2.0 6.1 3.6 3.6 0.7

2.1 10.3 10.7 8.3 7.7

1415-7 1415-20 1415-30 1415-50 1415-100

AE AE AE AE AE

0.6 0.6 0.5 0.1

0.3 0.6 0.7 0.7 0.7 0.8

5.6 7.4 9.0 1.6

2.2 6.8 9.9 10.4 8.9 7.2

1215-9 1215-12 1215-18 1215-30 1215-50 1215-84

0.5

0.2

2

3.8

STO 0.1 0.4 0.5

Foam Volume Ratio 30 min:l min. C0„ Extrac 0.4 0.5 0.3

1.0

2

30 min Foam Volume (cc) CO^ Extracted STO STO 6.4 1.1 5.3 9.7 6.3 8.3

Surfactant Foaming i n the Presence of West Texas F i e l d Stock Tank O i l at 40°C

AE AE AE AE AE AE

AE 1213-6.5

Surfactant AE 911-8 AE 911-12 AE 911-20

Table I I I .


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ι

8. BORCHARDTETAL.

177

Surfactantsfor CO Foam Flooding 2

EO/mole of parent alcohol and then gradually declined. Somewhat d i f f e r e n t behavior was observed using s u p e r c r i t i c a l C0 -extracted stock tank o i l which had a higher carbon number 26 vs 16) , a higher asphaltene content (1.52% vs 0.78%), and a higher combined acid and base number (0.85% vs 0.33) than the unextracted o i l (see above). The maximum foam volume was observed at a lower ethylene oxide content (for C , 20 moles of EO vs 30 moles of EO for unextracted o i l ) . The decline i n foam volume with further increases i n EO content was much more rapid i n the presence of C0 -extracted oil. This behavior was also observed for C alcohol ethoxylates and C alcohol ethoxylates. AE surfactants appeared to exhibit two modes of behavior. Generally foam volume did not decrease for AE surfactants containing less than ca 20 moles EO/mole surfactant when C0 -extracted stock tank o i l was used instead of stock tank o i l (Figure 2). However, at EO levels above 30 moles/mole surfactant, foam volume i n the presence of C0 -extracted stock tank o i l was less than i n the presence of stock tank o i l . These results imply that since residual crude o i l composition changes as i t undergoes extraction by injected C0 , the optimum C0 mobility control agent may change during the course of the C0 flood. 2

1 2

1 6

2


1 4

1 6

9 X 1

2

2

2

2

2

High Pressure Sight C e l l Studies Sight c e l l studies have been performed at 75°C and 2500 p s i g C0 pressure using AESo and AEGS surfactants. The foam s t a b i l i t y , as indicated by the 30 minute:1 minute foam volume r a t i o , as a funct i o n of the surfactant EO content i s shown i n Figure 4. In one atmosphere foaming tests i n the presence of decane, the 10 minute foam volume was taken as a measure of foam s t a b i l i t y (see above) and plotted against surfactant EO content i n Figure 4. The s i m i l a r geometry of the AESo and AEGS curves i n Figure 4 indicated that increasing the test pressure from 1 atmosphere to 2500 p s i g C0 did not a l t e r the e f f e c t of surfactant chemical structure on foam s t a b i l i t y . At both test pressures, increasing the EO content from 6 to 12 moles per mole AESo surfactant d i d not have a substantial e f f e c t on foam s t a b i l i t y . However, at both 1 atm and 2500 psig C0 pressure, an increase from 12 to 16 moles EO per mole AESo surfactant resulted i n a s i g n i f i c a n t increase i n foam s t a b i l i t y . The AEGS foam s t a b i l i t y at both 1 atmosphere and 2500 psig C0 increased steadily with increasing EO content of the surfactant. 2

2

2

2

Core Floods The surfactants (AEGS) which performed best i n the one atmosphere foaming experiments i n the presence of o i l , both refined and crude, prevented gravity override and viscous i n s t a b i l i t i e s enabling high pressure C0 to displace a l l the o i l i n t e r t i a r y f i r s t contact misc i b l e core floods i n a p i s t o n - l i k e manner.(1) In the absence of surfactant, gravity override was c l e a r l y observed. This would lead to a lower volumetric sweep e f f i c i e n c y , higher produced g a s : o i l r a t i o s , and lower o i l recovery at equivalent C0 volume i n j e c t i o n . (See "A CT Study of Surfactant-Induced Mobility Control for Carbon Dioxide" by S. L. Wellington and H. J . Vinegar, t h i s book.) 2

2





8. BORCHARDT ET AL.

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Surfactants for CO Foam Flooding 2

At the surfactant concentrations employed i n the core f l o o d ( l ) . there was no evidence of severe permeability reduction that would cause s u b s t a n t i a l l y reduced i n j e c t i v i t y . The surfactant d i d not cause viscous forces to dominate during immiscible t e r t i a r y carbon dioxide i n j e c t i o n . Apparently, the unmobilized o i l reduced the foam s t a b i l i t y while the surfactant reduced the i n t e r f a c i a l tension and therefore the C0 -brine c a p i l l a r y pressure s u f f i c i e n t l y to allow gravity e f f e c t s to dominate the flood, u i Downloaded by CALIFORNIA INST OF TECHNOLOGY on November 22, 2017 | http://pubs.acs.org Publication Date: July 20, 1988 | doi: 10.1021/bk-1988-0373.ch008

2

CONCLUSIONS Surfactant foaming properties are r e l a t e d to surfactant chemical structure parameters such as hydrophobe size, ethylene oxide chain length, and hydrophile functional group. Increasing the test pressure from one atmosphere to 2500 p s i g C0 d i d not a l t e r the e f f e c t of surfactant chemical structure on r e l a t i v e foaming performance. Surfactant foaming properties are r e l a t e d to o i l phase com p o s i t i o n . The composition of the residual o i l w i l l change i n the course of a C0 EOR project. The optimum C0 mobility control agent may thus change during the course of the project. Of the surfactants tested, AEGS surfactants produced the most persistent foams at high s a l i n i t y and elevated temperatures i n the presence of synthetic and crude o i l s ( i n one atmosphere experi ments ). 2

2

2

Acknowledgments The authors wish to acknowledge the important contributions of David Haseltine, Craig Yates and Tanya Balthazar who performed many of the one atmosphere foaming experiments and of Eugene F. Lutz, J. Dan Paiz and T. Α. Β. M. Bolsman who synthesized some of the test surfactants. The authors would l i k e to thank S h e l l Development Company for permission to publish this work. Literature Cited 1.

Wellington, S. L. and Vinegar, H.J. "CT Studies of Surfactant-Induced CO Mobility Control," paper SPE 14393 presented at the 60th Annual Technical Conference and Exposition of the Society of Petroleum Engineers of AIME, Las Vegas, September 22-25, 1985. Wellington, S. L . , Reisberg, J., Lutz, E. F . , and Bright, D. B. U. S. Patent 4502538, (1985). Bikerman, J. J. "Foams," Springer-Verlog, New York (1973), p. 85. Borchardt, J. Κ., Bright, D. Β . , Dickson, Μ. Κ., Wellington, S. L. Paper SPE 14394 presented at the 60th Annual Technical Conference and Exhibition of the Society of Petroleum Engineers of AIME, Las Vegas, September 22-25, 1985. Patton, J. T. "Enhanced Oil Recovery by CO Foam Flooding," U. S. DOE Report, Contract No. DE-AC21-78MC03259 (February 1980). 2

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Heller, J. P. "Reservoir Application of Mobility Control Foams in CO Floods, paper SPE/DOE 12644 presented at the SPE/DOE Fourth Joint Symposium on Enhanced Oil Recovery, Tulsa, Oklahoma, April 15-18, 1984. Schmitt, K. D. "The Hydrolytic Stability of Ethoxylated Alkyl Sulfates," paper INDE-14 presented at the 184th National Meeting of the American Chemical Society, Kansas City, Missouri, September 12-17, 1982. Bernard, G. G . , Holm, L. W., and Harvey, C. P. Soc. Pet. Eng. J., 1980, 281-292. Wellington, S. L. and Vinegar, H. J. J. Pet. Technol., 1987, 36, 885-898. 2

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Received January 29, 1988


Surfactant-Based Mobility Control - American Chemical Society

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