This invention relates to a fluid drive oil recovery process which utilizes an injection of CO.sub.2, surfactant and water into subterranean oil reservoir. More particularly, the invention relates to such a process in which the surfactant selected for use is a particular member of a relatively highly chemically stable and salt-tolerant class of surfactants and is uniquely suited for use in the reservoir to be treated.
Numerous patents have been issued on materials and techniques which are pertinent to an oil recovery process that utilizes an injection of CO.sub.2, surfactant and water. The U.S. Pat. Nos. 2,226,119; 2,233,381 and 2,233,382 describe polyalkoxylated alcoholic or phenolic surfactants which are generally useful in aqueous liquid fluid drive oil recovery processes. U.S. Pat. No. 2,623,596 indicates that an increased oil recovery may be obtained by a fluid drive process which injects highly pressurized CO.sub.2. U.S. Pat. No. 3,065,790 indicates that, in a fluid drive process, the cost effectiveness of highly pressurized CO.sub.2 may be increased by injecting a slug of the CO.sub.2 ahead of a cheaper drive fluid. U.S. Pat. No. 3,330,346 indicates that almost any process for forming foam within a reservoir may be improved by using as the surfactant a polyalkoxylated alcohol sulfate of an alcohol containing 10 to 16 carbon atoms. U.S. Pat. No. 3,342,256 indicates that, in a fluid drive process, the oil-displacing efficiency of a CO.sub.2 slug may be increased by including water and a foaming surfactant within that slug. U.S. Pat. No. 3,529,668 indicates that, in a fluid drive process, the efficiency of a slug of foamed CO.sub.2 may be increased by displacing it with specifically proportioned alternating slugs of gas and liquid. U.S. Pat. No. 4,088,190 indicates that, in a fluid drive process, the heat stability and durability of a CO.sub.2 foam may be increased by using an alkyl sulfoacetate surfactant. U.S. Pat. No. 4,113,011 indicates that in a CO.sub.2 foam drive, the problems of low salt tolerance with are typical of both the surface-active sulfates of polyalkoxylated alcohols containing 10 to 16 carbon atoms recommended by U.S. Pat. No. 3,330,346 and the alkyl sulfoacetate surfactants recommended by U.S. Pat. No. 4,088,190 may be avoided by using a surfactant sulfate of a polyalkoxy alcohol containing only 8 or 9 carbon atoms and injecting that surfactant ahead of the CO.sub.2.