Surfactant-Based Mobility Control - American Chemical Society

Chapter 7

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Foam Stability: Effects of Oil and Film Stratification 1

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D. T. Wasan, A. D. Nikolov , D. D. Huang , and D. A. Edwards Department of Chemical Engineering, Illinois Institute of Technology, Chicago, IL 60616 Foam stability in the presence of Salem crude o i l and pure hydrocarbons is investigated as a function of chain length of α - o l e f i n sulfonates and electrolyte concenra tion. Interactions between aqueous foam films and emulsified o i l droplets are observed using transmitted light, incident light interferometric and differential interferometric microscopic techniques. Foam destabili zation factors are identified including the pseudo emulsion film tension and the surface and interfacial tension gradients. Results from foam-enhanced o i l re covery experiments in Berea Sandstone cores are pre sented using the combined gamma ray/microwave absorp tion technique to measure dynamic fluid satruation profiles. Three phase foam s t a b i l i t y , as has been discussed by numerous authors i s of great p r a c t i c a l s i g n i f i c a n c t (1-14). However, despite the recognized significance, the mechanisms by which o i l affects foam s t a b i l i t y are s t i l l under investigation. The e f f e c t of o i l upon foam s t a b i l i t y has been explained i n rather general terms through the mechanism of o i l spreading phenomena, but the reason why the o i l droplets spread and the f i l m between the o i l droplets and a i r bubbles breaks has not been d i s cussed. Our objective i n this study i s to elucidate the complex phenome na occurring during the process of three phase foam thinning, to i d e n t i f y the interaction mechanisms between the o i l droplets, the thinning foam f i l m and the Plateau-Gibbs borders and the role of surface and i n t e r f a c i a l tension gradients i n foam s t a b i l i t y , and to examine the implications upon crude o i l displacement by foam i n pourous media.

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Current address: University of Sofia, 1126 Sofia, Bulgaria Current address: Polaroid Corporation, Bedford, MA 01730

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0097-6156/88/0373-0136$07.75/0 ο 1988 American Chemical Society In Surfactant-Based Mobility Control; Smith, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

7. WASAN ET AL.

137

Foam Stability: OU and Film Stratification

During the process of three phase foam thinning, three d i s t i n c t films may occur: foam films (water f i l m between a i r bubbles), emul sion films (water between o i l droplets) and pseudoemulsion films (water f i l m between a i r and o i l droplets) (Figure 1). To study the behavior of these films and p a r t i c u l a r l y the o i l droplet-droplet, o i l d r o p l e t - a i r bubble and o i l droplet-foam frame interactions i t i s necessary to u t i l i z e numerous microscopic techniques, including transmitted l i g h t , microinterferometric, d i f f e r e n t i a l interferometrie and cinemicrographic microscopy.


EXPERIMENTAL Surfactant-Oil-Electrolyte Systems. In t h i s study we used as sur factants alpha-olefin sulfonates C , C.,, and C- (anionic surfac tants, product of Ethyl Corp.) and Enordet AE 1215-30 (nonionic sur factant, product of S h e l l Development Co.). For all_measurements, the surfactant concentration was chosen at 3.16 χ 10~ mol/1, several times above the c r i t i c a l micelle concentration (cmc). These p a r t i c u l a r surfactants (and concentrations) were chosen on the basis of i n d u s t r i a l applications (6,7,15). As o i l phases we used η-octane (Fisher S c i . Co. reagent grade Lot 746833 class IB) and n-dodecane (Fisher S c i . Co. p u r i f i e d grade Lot 852154), both chosen for their well-defined structure and Salem crude o i l , chosen for i t s p r a c t i c a l value. E l e c t r o l y t e was chosen as NaCl, at two concentrations 0.17 mol/1 (1 wt%) and 0.51 mol/1(3 wt%). In each study the oil-water system was preequilibrated f o r one week. 12

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Macroscopic Observations of Three Phase Foam Structure. In Figures 2 and 3 are shown foam drainage r e s u l t s i n the presence of Salem crude o i l with the surfactants CÂOS and C-.AOS at 1 wt% NaCl. obtained from the transmitted l i g h t microscope. Surfactant chain length i s c l e a r l y seen to be a s i g n i f i c a n t factor (compare Figure 2 with Figure 3). In Figure 2 the process of coalescence between a samll a i r bubble (white c i r c u l a r object entering the movie frame from the upper middle portion of the frame) and an o i l lens on large bubble surface (the thick dark edge of the large white object i n the upper portion of the movie frame i s the o i l lens on the large bubble surface) i s i l l u s t r a t e d for the C ^ system. After a c e r t a i n thickness the "pseudoemulsion f i l m Formed between the o i l lens and the a i r bubble surface ruptures and the o i l phase spreads on the surface, forming an o i l "bridge" between small and large bubble surfaces. The "pseudoemulsion" f i l m i s therefore unstable for the C system. In Figure 3, movie frames capturing the foam structure and dynamics of the C^^ AOS system reveal that the pseudoemulsion films formed between the o i l droplets and a i r bubble surface are stable enough to allow the eventual migration of the droplets to the GibbsPlateau border where at a c e r t a i n c a p i l l a r y radius they coalesce (Figure 3). Further increasing the curvature r a d i i of the Plateau borders r e s u l t s i n a rupturing of the pseudoemulsion f i l m i n the borders. Rupture of the pseudoemulsion f i l m allows the o i l to A 0 S

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A 0 S

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


138

SURFACTANT-BASED MOBILITY CONTROL

Figure 1. surface.

Pseudoemulsion f i l m between o i l droplet and air/water

Figure 2. Spreading of Salem crude o i l between two bubble surfaces f o r C..AOS with 1 wt% NaCl.


WASANETAL.

Foam Stability: Oil and Film Stratification


7.

Figure 3. NaCl.

Two dimensional foam drainage for C

AOS with 1 wt% 1 6


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spread, disturbing the mechanical equilibrium between the foam lamellae and border such that the entire foam frame breaks (Figure 4). Therefore, the i n t e r a c t i o n between the o i l droplets i n the Plateau borders and l i q u i d f i l m plays an important role i n determining foam stability. Macroscopic three phase foam observations therefore reveal that C.. AOS produces a more stable foam i n the presence of o i l than AOS. Microscopic Observations of Three Phase Foam Structure. We w i l l now discuss observations of the microscopic o i l droplet-foam i n t e r a c tions, and observations regarding the attachment of o i l droplets to the air-water surface. O i l Droplet-Foam Film Interaction. The commonly known mechanism i n the l i t e r a t u r e by which o i l droplets affect foam s t a b i l i t y i s , as previously mentioned, the mechanism of o i l droplet spreading (8). I t i s suggested that during the process of foam lamella thinning, the o i l droplets are squeezed between the f i l m surface and spread on one of the f i l m surfaces ( i n the form of lenses) eventually then spreading also on the second f i l m surface. F i n a l l y , i t i s assumed that an " i s l a n d " of o i l i s formed which breaks the lamella (thick f i l m ) . To test this hypothesis, we designed two microscopic i n t e r f e r o metric experiments (16-17). The f i r s t experiment was to form a f i l m with a 0.02 cm radius from aqueous surfactant solutions of and C AOS which were preequilibrated with Salem crude o i l . During the time of p r e e q u i l i b r a t i o n part of the crude o i l formed a stable o i l i n water emulsion (more pronounced for AOS). Prior to extracting the l i q u i d from the double concave meniscus, i t was observed that f l o a t i n g lenses of crude o i l were spread upon the foam surfaces. A f t e r withdrawing l i q u i d from the f i l m , the o i l droplets and the f l o a t i n g lenses on the f i l m surfaces migrated from the area of f i l m thinning to the meniscus. Following the droplet migration (after a f i l m thickness of lOOnm) the process of thinning displayed two d i f f e r e n t phenomena, depending upon the e l e c t r o l y t e concentrat i o n . At an e l e c t r o l y t e concentration less than 1 wt %, the f i l m had two thickness t r a n s i t i o n s . The f i r s t from 50nm to 35nm and the second from 35nm to 19nm, which i s the f i n a l equilibrium thickness. The steps of these two transitions were approximately equal and independent of the f i l m radius (Figure 5). At one-to-one e l e c t r o l y t e concentration higher than 1 wt % the f i l m thickness changed by a single step t r a n s i t i o n and was dependent upon the f i l m radius (Figure 6). For C AOS there was found only one t r a n s i t i o n of the foam f i l m both for the systems with and without e l e c t r o l y t e . The second type of microscopic interferometric experiment was devised to study the thinning of an emulsion f i l m . For an emulsion f i l m the dispersed o i l phase may be i n contact with the f i l m surfaces for a longer time due to the diminished i n t e r f a c i a l tension, therefore the thinning phenomena of emulsion films d i f f e r s from that of foam f i l m s . A 0 S

fi


WASANETAL.

Foam Stability: OU and Film Stratification


7.

Figure 4. oil.

Breakup of foam frames i n the presence of Salem crude


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142


Figure 5. Photocurrent formed with C..AOS.

time interferogram of the foam f i l m


WASAN ET AL.

Foam Stability: Oil and Film Stratification


7.

Figure 6. Photocurrent vs. time interferogram of the foam f i l m formed with C AOS and 1 wt% NaCl. 1/:


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144


Using both η-octane and n-dodecane as the dispersed phase i n place of the a i r , we observed that f o r both C-« * ^ AOS, with and without e l e c t r o l y t e , the time-scale of thinning increased at least two-fold over the time-scale of the foam thinning. For C^g AOS without e l e c t r o l y t e , again there were two thickness transitions although the stepwise transitions seemed somewhat greater than those for the foam f i l m . The f i n a l thickness of the emulsion f i l m was also greater than that of the foam f i l m (about 20nm). After about 10 minutes following the f i n a l f i l m thickness, the f i l m ruptured. At 1 wt % e l e c t r o l y t e f o r C- AOS there was one step t r a n s i t i o n which was dependent upon f i l m raaius as i n the case of the foam f i l m . Unlike the case without e l e c t r o l y t e the emulsion f i l m ruptured dur ing the f i l m t r a n s i t i o n . Identical f i l m t r a n s i t i o n results were obtained for C ^ 2 « A

0

S

& η

I

î


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Figure 15. C A03.

O i l saturation during foam-enhanced o i l recovery with

Distance along the Length of the Core (inches)


r

Ο

=

2

ο

ο

W

2 Ο

ϊ

Ά

S! ο 52

*>

01 00


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Figure 16. Pressure data f o r foam-enhanced o i l recovery with C AOS, CÂOS and CÂOS.

Pore Volume Injected (PV)


ϊ

ι

I a

ϊI

i

$

160



point dropped below 20%, while saturation for positions 2-4 dropped to 0.28 - 0.36. The o i l saturation for the rest of the core remained v i r t u a l l y unchanged during the foam flooding process. By comparison, Figure 14 demonstrates that the o i l saturation p r o f i l e for CÂOS i s d i f f e r e n t than that of C,«A0S. The curves are steeper and hence the f r o n t a l speed of o i l i n this case i s higher. At 1 pore volume of surfactant solution injected, the o i l saturation at the f i r s t point dropped to about 15% and to about 38% by position 4. In the case of C ÂOS the o i l saturation at the f i r s t point dropped below 10% and to about 30% at p o s i t i o n 4. The CÂOS system displays the fastest propagation rate of o i l (Figure 15). Table 2. O i l Recovery Results from Produced F l u i d Analyses for C , C . and C AOS under Constant Pressure

C

12

3

2

1

Experiment

C

14

C

16

74.0 71.5 73.0 I n i t i a l O i l Saturation 41.5 39.8 42.1 Waterflood O i l Saturation 39.5 37.0 39.0 Surfactant Flood O i l Saturation 2.7 3.9 4.3 % Recovery* Foam Flood O i l Saturation 28.5 22.5 23.5 21.6 20.2 14.4 % Recovery* 23.0 35.0 39.0 Break Through Time (min) * Percent o i l recovery i s based on the i n i t i a l o i l saturation Table 3.

O i l Recovery Results from Produced F l u i d Analyses f o r C , C and C AOS under Constant Flow Rate 12

1 4

1 6

C

I n i t i a l O i l Saturation Waterflood O i l Saturation Surfactant Flood O i l Saturation % Recovery* Foam Flood O i l Saturation % Recovery* Break Through Time (min)

12

74.0 42.1 39.8 3.1 33.9 8.0 36.0

6

5

4

Experiment

C

14

73.8 43.2 40.6 3.5 33.1 10.2 48.0

C

16

75.2 43.5 41.7 2.4 30.6 14.8 62.0

* Percent o i l recovery i s based on the i n i t i a l o i l saturation Figure 16 shows the pressure drop across the core as a function of pore volume of nitrogen gas injected. The highest pressure drop i s always observed before the gas breakthrough ( i t i s worth noting, for the CÂOS system, the faster propagation rate of o i l i s accompanied by a more rapid increase i n the pressure drop). Our foam-enhanced o i l recovery experiments i n Berea Sandstones showed f o r the f i r s t time a s t r i k i n g c o r r e l a t i o n between basic foam


7. WASAN ET AL.

Foam Stability:Oiland Film Stratification

161

properties and o i l displacement e f f i c i e n c i e s of three d i f f e r e n t foam ing agents: C..AOS, C AOS and C,,AOS. w


CONCLUDING REMARKS The interactions between an o i l phase and foam lamellae are extremely complex. Foam d e s t a b i l i z a t i o n i n the presence of o i l may not be a simple matter of o i l droplets spreading upon foam f i l m surfaces but may often involve the migration of emulsified o i l droplets from the foam f i l m lamellae into the Plateau borders where c r i t i c a l factors, such as the magnitude of the Marangoni effect i n the pseudoemulsion f i l m , the pseudoemulsion f i l m tension, the droplet s i z e and number of droplets may a l l contribute to d e s t a b i l i z i n g or s t a b i l i z i n g the three phase foam structure. The s t a b i l i t y of emulsion and foam films have also been found dependent upon the m i c e l l a r microstructure within the f i l m . E l e c t r o lyte concentration, and surfactant type and concentration have been shown to d i r e c t l y influence this microstructure s t a b i l i z i n g mechanism. The e f f e c t of o i l s o l u b i l i z a t i o n has also been discussed. The pre ceding s t a b i l i z i n g / d e s t a b i l i z i n g mechanisms for three phase foam systems have been shown to predict the effectiveness of aqueous foam systems for displacing o i l i n enhanced o i l recovery experiments i n Berea Sandstone cores. F i n a l l y we should comment that i t i s necessary to employ i n the c a l c u l a t i o n of the spreading c o e f f i c i e n t (which i s often used as a s t a b i l i t y c r i t e r i o n ) accurately measured values of the various ten sions operative i n the "pseudoemulsion" f i l m to determine whether o i l i s spreading or nonspreading i n the three phase foam structure. We have found that the d i f f e r e n t i a l interferometrie technique to be p a r t i c u l a r l y useful i n this regard (32). ACKNOWLEDGMENTS This study was supported by the National Science Foundation and partly by the U. S. Department of Energy. LITERATURE CITED 1. 2. 3. 4. 5. 6.

Lau, H.C. and O'Brien, S.M.: New paper submitted SPE 15668, A p r i l , 1986. Minssaiux, L.: JPT (Jan. 1974), 100-108. Farouq, Ali, S.M. and Selby, R . L . : O i l & Gas J. (Feb. 3, 1986), 57-63. Bernard, G . G . and Holm, L.W.: Soc. Petr. Eng. J. (Dec. 1915), 295-300. Raza, S.H. Soc. Petr. Eng. J. (Dec. 1970), 328-336. Lau, H.C., and O'Brien, S.M.: paper SPE 14391, presented at the

1985 SPE Annual Technical Conference and Exhibition, Las Vegas, Sept. 22-25.

7.

8.

Hu, P.C., Tuvell, M . E . and Bonner, G.A.: Paper SPE/DOE 12660 presented at the Fourth Symposium on Enhanced O i l Recovery, April 15-18, 1984. Prince, Α . : Seminar presented at the Illinois Institute of Tech nology, (June, 1985).


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9.

Dunning, Ν . , Eakin, J.L. and Walker, C . L . : Monogr. 11, U.S. Bureau of Mines (1961) 38-47. Pletnev, M. Yu., Trapeznikov, A . A . : In "Foams Their Generation and Applications," presented at the second All-union conference [ in USSR (in Russian)] Shebekino (ed.) (1979) 33-52. Roberds, Κ., Axberg, C . , Osterlund, R.: J. Coll. Int. S c i . , (1977) 62, 264-272. Ross, S.: Chem. Eng. Prog. (1967) 41-47. Perri, J.M.: Foams Theory and Industrial Applications, J.J. Bikerman (ed.), Reinhold, New York (1953) 195-211. Fried, A.N.: U.S. Bur. Mines, Rep. Inv. 5866. (1961). Shell Chemical Company, "Enordet EOR Surfactants," Houston. (1984). Manev, E . D . , Sazdanova S.V., Rao, A.A. and Wasan, D.T.: J. Disp. Sci. Tech. (1982) 3, 435-463. Rao, Α.A., Wasan, D.T. and Manev, E.D.: Chem. Eng. Commun. (1982 15, 63-81. Nikolov, Α . , Kralchevsky, P . , Ivanov, I . : J. Coll. Inter. Sci. (1986) 112, 122-132. Kao, K . , Ph.D. Thesis in progress, Illinois Institute of Tech nology, Chicago (1987). Huang, D.D., Nikolov, A . D . , and Wasan, D.T.: Langmuir (1986) 2, 672-683. Wasan, D.T., Perl, J.P., and Milos, F . S . : paper SPE8327 pre sented at the 1979 Fall Technical Conference of the Soc. Pet. Eng., Las Vegas, N.M. Reiss-Husson, F. and Luzzati, V . : J. Phys. Chem. (1964) 68, 3504-3511. Efremov, I . F . : "Periodic Colloid Structure" in "Surface and Colloid Science," E. Matijevic (ed.), Wiley Inter. S c i . , New York (1976) 85. Bruil, H.G., and Lyklema, J.: J. Nature Phys. Sci.(1971) 223, 19-20. Kruglyakov, P.M. and Rovin, I . G . : "Physical Chemistry of Black Hydrocarbon Fioms - Biomolecular Lipid Membrane," Nauka, Moscow, (1978) (in Russian). Manev, E . D . , Sazdanova, S.V. and Wasan, D.T.: J. Disp. Sci. Tech. (1984)5, 111-117. Nikolov, A.D. and Wasan, D.T.: "Layered Structures in Thin Liquid Films: Micellar Interactions and Microstructure Effects on Film Stability," (in preparation). Wasan, D.T. and Nikolov, A.D.: "Micelles Interaction in Foam Film Formed from Nonionic Surfactants," (in preparation). Wasan, D.T. and Nikolov, A.D., paper presented at the Sixth International Symposium on Surfactants in Solution, New Delhi, August, 1986. Verwey, E . J . and Overbeek, J.G.: "Theory of Stability of Lypophobic Colloids", Elsevier, Amsterdam (1948). Marangoni, C.: Nuovo Cinento, (1978) Ser 3, 50, 97, 192. Nikolov, A . D . , Wasan, D.T., Huang, D.D., and Edwards, D.A., SPE Preprint 15443, paper presented at the SPE Meeting, New Orleans, L a . , October 5-8, 1986.

10. 11. 12. 13.


14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.

26. 27. 28. 29. 30. 31. 32.

Received March 3, 1988


Surfactant-Based Mobility Control - American Chemical Society

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