Waterflooding employing thickened surfactant solutions

Claim 1

In a method for the recovery of oil from a subterranean oil reservoir having a temperature of at least 90° F. and penetrated by spaced injection and production systems wherein an aqueous fluid is introduced into said reservoir via said injection system to displace oil to said production system, the improvement comprising: employing as at least a portion of the fluid introduced into said injection system a thickened aqueous liquid having a salinity within the range of 5-18 weight percent and containing a mixture of at least two water-soluble sulfonated polyethoxylated aliphatic alcohols of different HLB values and whereby said mixture increases the viscosity of said aqueous liquid to a value greater than the viscosity of said aqueous liquid containing an equal amount of either of said sulfonated polyethoxylated aliphatic alcohols alone, said mixture having an average HLB within the range of 10.0-14 and said sulfonated polyethoxylated aliphatic alcohols being characterized by the formula: R(OC.sub.2 H.sub.4).sub.n OC.sub.3 H.sub.6 SO.sub.3.sup.-M+(I) wherein R is an aliphatic hydrocarbon group having an average of from 16 to 20 carbon atoms, n is at least 2, and M is an alkali metal, ammonium, or substituted ammonium ion.