Oil recovery process employing a hydrocarbon slug and a thickened

Abstract

The recovery of oil by surfactant waterflooding involving the injection of a hydrocarbon slug followed by a thickened aqueous surfactant slug. The hydrocarbon slug is injected into the reservoir in an amount of at least 0.02 pore volume and has a viscosity less than that of the reservoir oil. The thickened surfactant slug comprises an aqueous solution of a surfactant system which includes an organic sulfonate surfactant and which functions to increase the viscosity of the aqueous liquid to a value at least as great as the viscosity of the reservoir oil while decreasing the oil-water interfacial tension. The surfactant slug may include one or more organic sulfonates, either alone or in mixture with a water-soluble aliphatic alcohol.