Oil recovery by surfactant-alcohol waterflooding

Claim 1

In a method for the recovery of oil from a subterranean oil reservoir penetrated by spaced injection and production systems in which an aqueous fluid having a salinity of at least 5 percent by weight and a divalent metal ion concentration of at least 0.5 percent by weight is introduced into said reservoir via said injection system to displace oil to said production system, the improvement comprising employing in said fluid the following: (a) a mixture of a sulfobetaine surfactant and a preferentially oil-soluble aliphatic alcohol cosurfactant, said surfactant and cosurfactant being present in said fluid in amounts sufficient to lower the interfacial tension of water in said fluid and oil in said reservoir; (b) a thickening agent which is a quaternary ammonium compound containing at least one hydrocarbyl group having 16 to 20 carbon atoms, said thickening agent being present in said fluid in an amount sufficient to achieve a viscosity of at least a portion of said fluid of about 1 to 4 times the viscosity of the reservoir oil; and (c) a sacrificial agent which is an organic quaternary ammonium compound wherein the organic groups are alkyl groups containing 1 to 4 carbon atoms, said sacrificial agent being present in said fluid in an amount sufficient to reduce loss of said surfactant and said thickening agent in said reservoir.