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Foams as mobility control agents
Foams, as a conformance improvement technology for use during gas flooding (e.g., steam, CO2, and miscible gas flooding), have historically been most widely studied and applied when the foams are to be used in the form of a “viscosity-enhancing” mobility-control agent that is injected from the injection-well side. Because relatively large volumes of foam are required and because the foam must be propagated significant distances in the reservoir, applying foams for mobility control has proven technically and economically challenging. This article discusses applications and challenges associated with foams as mobility control agents.
Reducing gas channeling and override
As discussed in Foam properties, the low effective density of most mobility-control foams, which are used during a gas flood such as a steam or CO2 flood, provides a driving force for the foam to flow and be desirably placed in the upper reservoir vertical interval where the offending gas override is occurring and where the foam will be most effective at countering the negative impact of the gas override. Shi and Rossen describes an “improved” surfactant-alternating-gas foam injection process to control gravity override during gas flooding projects.
CO2 foams are considered to be an effective mobility-control agent candidate for use during CO2 flooding to improve CO2 sweep efficiency. This includes the use of “foams” formulated with supercritical and dense CO2. Surfactant selection and surfactant adsorption/retention losses are particularly critical parameters to the successful economic application of CO2 foams during CO2 flooding operations. The exploitation of relatively low-cost CO2 foams formulated with surfactant concentrations below the critical micelle concentration has been suggested. The sequential or water alternating gas (WAG) injection of the CO2 and the foaming solution is often preferred for the injection of mobility-control CO2 foam. (see Foam properties)
Use of steam foams has been studied extensively and has been reduced to field practice as a technique to improve vertical and areal sweep efficiency and to reduce steam channeling and override during steam flooding that is being applied to shallow heavy-oil reservoirs. The steam foam process consists of adding surfactant, with and without the addition of a noncondensable gas, to the injected steam. Based on the combined findings of theory, laboratory studies, and field performance, it has been determined that steam foams are normally more effective when a small amount of a noncondensable gas, such as nitrogen, is incorporated into a steam-foam formula. Steam foams have been used in conjunction with both continuous and cyclic steam injection.
As with foams for CO2 flooding, the effectiveness and the economics of the steam-foam process are critically dependent on surfactant adsorption and retention. Unlike CO2 foams, surfactant thermal stability is also a critical issue. Alpha-olefin sulfonates, along with petroleum sulfonates, are the surfactants that have been favored for use in conformance improvement steam foams. Borchardt and Strycker have studied commercial olefin sulfonate surfactants to determine what the optimum chemistry should be in terms of favorable surfactant performance in foams for steam flooding applications.
To mitigate the destabilizing effect of oil on steam foam, one proposed strategy is to inject a prefoam surfactant slug to mobilize the residual oil ahead of the steam foam. Steam foams have been extensively applied in conjunction with the heavy oil production operations in Kern County, California, US. The application of steam foam in Kern County has been considered a technical success, but its economic success is suspect.
Miscible gas flooding
Although it would appear that foams would be well suited to impart mobility control and to improve sweep efficiency during miscible gas flooding (in a similar manner as during CO2 and steam flooding), relatively few papers have appeared in the literature about this application of conformance improvement foams, especially the actual field application of foams for use in conjunction with miscible gas flooding. Mannhardt and Novosad studied the adsorption of foaming surfactants to be used with hydrocarbon-miscible flooding in reservoirs with high salinities. Two sources discuss the application of foams for use during hydrocarbon miscible flooding in Canada.
Sizing volume injected
The volume of foam that should be injected during application, as a mobility control agent in conjunction with gas flooding, is a subject that lacks good and sound engineering guidelines. Thus, the sizing of such foam applications must be custom design based on previous experience with similar applications, and/or be based on empirical guidelines. It does not make sense to design the depth of foam placement to be greater than the distance the foam can propagate through the reservoir.
Polymer enhanced foams
The addition of a water-soluble polymer to the foaming solution has been suggested as a means to increase stability of the foam, increase the effective viscosity and structure of foams, and improve the oil tolerance of foams. The possible use of polymer-enhanced foams to treat fracture conformance problems has been suggested. Polymer enhanced foams formulated with high-molecular weight (MW) acrylamide polymers have been noted to be rheologically shear-thinning fluids that substantially aid in the injectivity of preformed polymer enhanced foams.
Potential disadvantages of the use of polymer enhanced foams are
- Reduced injectivity of preformed polymer enhanced foams as compared with conventional foams
- Possible increased difficulty in propagating the polymer enhanced foam through matrix reservoir rock
- Somewhat increased operational and chemical complexity in applying polymer-enhanced foams as compared with conventional foams.
The original interest in foams as mobility control agents has faded somewhat and interest in the use of conventional foams as fluid-flow blocking agents has also faded because foam fluid-flow blocking treatments are operationally and chemically relatively complex and polymer gels are considered by many petroleum engineers to be more effective, durable, and stronger.
- Shi, J.-X. and Rossen, W.R. 1998. Improved Surfactant-Alternating-Gas Foam Process to Control Gravity Override. Presented at the SPE/DOE Improved Oil Recovery Symposium, Tulsa, Oklahoma, 19-22 April 1998. SPE-39653-MS. http://dx.doi.org/10.2118/39653-MS
- Casteel, J.F. and Djabbarah, N.F. 1988. Sweep Improvement in CO2 Flooding by Use of Foaming Agents. SPE Res Eng 3 (4): 1186–1192. SPE-14392-PA. http://dx.doi.org/10.2118/14392-PA
- Tsau, J.-S., Yaghoobi, H., and Grigg, R.B. 1998. Smart Foam to Improve Oil Recovery in Heterogeneous Porous Media. Presented at the SPE/DOE Improved Oil Recovery Symposium, Tulsa, Oklahoma, 19-22 April 1998. SPE-39677-MS. http://dx.doi.org/10.2118/39677-MS
- Heller John, P. 1994. CO2 Foams in Enhanced Oil Recovery. In Foams: Fundamentals and Applications in the Petroleum Industry, 242, 5, 201-234. Advances in Chemistry, American Chemical Society. http://dx.doi.org/10.1021/ba-1994-0242.ch005.doi:10.1021/ba-1994-0242.ch005
- Di Julio, S.S. and Emanuel, A.S. 1989. Laboratory Study of Foaming Surfactant for CO2 Mobility Control. SPE Res Eng 4 (2): 136-142. SPE-16373-PA. http://dx.doi.org/10.2118/16373-PA
- Stevens, J.E. 1995. CO2 Foam Field Verification Pilot Test at EVGSAU: Phase IIIB--Project Operations and Performance Review. SPE Res Eng 10 (4): 266-272. SPE-27786-PA. http://dx.doi.org/10.2118/27786-PA
- Prieditis, J. and Paulett, G.S. 1992. CO2-Foam Mobility Tests at Reservoir Conditions in San Andres Cores. Presented at the SPE/DOE Enhanced Oil Recovery Symposium, Tulsa, Oklahoma, 22-24 April 1992. SPE-24178-MS. http://dx.doi.org/10.2118/24178-MS
- Kuhlman, M.I., Falls, A.M., Hara, S.K. et al. 1992. CO2 Foam With Surfactants Used Below Their Critical Micelle Concentrations. SPE Res Eng 7 (4): 445-452. SPE-20192-PA. http://dx.doi.org/10.2118/20192-PA
- Hirasaki, G.J. 1989. The Steam-Foam Process. J Pet Technol 41 (5): 449–456. SPE-19505-PA. http://dx.doi.org/10.2118/19505-PA
- Isaacs, E.E., Ivory, J., and Green, M.K. 1994. Steam-Foams for Heavy Oil and Bitumen Recovery. In Foams: Fundamentals and Applications in the Petroleum Industry, 242, 6, 235-258. Advances in Chemistry, American Chemical Society. http://dx.doi.org/10.1021/ba-1994-0242.ch006.doi:10.1021/ba-1994-0242.ch006
- Hamida, F.M. et al. 1992. Further Characterization of Surfactants as Steamflood Additives. In Situ 16 (2): 137.
- Borchardt, J.K. and Strycker, A.R. 1997. Olefin Sulfonates for High Temperature Steam Mobility Control: Structure - Property Correlations. Presented at the International Symposium on Oilfield Chemistry, Houston, Texas, 18-21 February 1997. SPE-37219-MS. http://dx.doi.org/10.2118/37219-MS
- Karin, M. and Jerry, J.N. 1994. Adsorption of Foam-Forming Surfactants for Hydrocarbon-Miscible Flooding at High Salinities. In Foams: Fundamentals and Applications in the Petroleum Industry, 242, 7, 259-316. Advances in Chemistry, American Chemical Society. http://dx.doi.org/10.1021/ba-1994-0242.ch007.doi:10.1021/ba-1994-0242.ch007
- Chad, J., Malsalla, P., and Novosad, J.J. 1988. Foam Forming Surfactants In Pembina/Ostracod 'G' Pool. Presented at the Annual Technical Meeting, Calgary, Alberta, Jun 12 - 16, 1988 1988. PETSOC-88-39-40. http://dx.doi.org/10.2118/88-39-40
- Liu, P.C. and Besserer, G.J. 1988. Application of Foam Injection in Triassic Pool, Canada: Laboratory and Field Test Results. Presented at the SPE Annual Technical Conference and Exhibition, Houston, Texas, 2-5 October 1988. SPE-18080-MS. http://dx.doi.org/10.2118/18080-MS
- Kabir, A.H. 2001. Chemical Water and Gas Shutoff Technology—An Overview. Presented at the SPE Asia Pacific Improved Oil Recovery Conference, Kuala Lumpur, 8–9 October. SPE-72119-MS. http://dx.doi.org/10.2118/72119-MS
- Minssieux, L. 1974. Oil Displacement by Foams in Relation to Their Physical Properties in Porous Media. J Pet Technol 26 (1): 100–108. SPE-3991-PA. http://dx.doi.org/10.2118/3991-PA
- Sydansk, R.D. 1994. Polymer-Enhanced Foams Part 1: Laboratory Development and Evaluation. SPE Advanced Technology Series 2 (2): 150–159.
- Zhu, T., Strycker, A., Raible, C.J. et al. 1998. Foams for Mobility Control and Improved Sweep Efficiency in Gas Flooding. Presented at the SPE/DOE Improved Oil Recovery Symposium, Tulsa, Oklahoma, 19-22 April 1998. SPE-39680-MS. http://dx.doi.org/10.2118/39680-MS
- Ye, Z., Pu, W., Zhang, S. et al. 1997. Laboratory Study On Profile Modification By Using Foamed Polymer Solution. Presented at the Annual Technical Meeting, Calgary, Alberta, Jun 8 - 11, 1997 1997. PETSOC-97-128. http://dx.doi.org/10.2118/97-128
- Romero, C., Alvarez, J.M., and Müller, A.J. 2002. Micromodel Studies of Polymer-Enhanced Foam Flow Through Porous Media. Presented at the SPE/DOE Improved Oil Recovery Symposium, Tulsa, Oklahoma, 13-17 April 2002. SPE-75179-MS. http://dx.doi.org/10.2118/75179-MS
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