Oil recovery method employing alternate slugs of surfactant fluid and

Abstract

Disclosed is a petroleum recovery method useful for recovering petroleum from subterranean formations containing water having high salinity and/or divalent ion concentration, employing an aqueous surfactant-containing fluid which is designed to effect low surface tension displacement of petroleum in the formation in the presence of high salinity water. The improvement comprises injecting the total desired volume of surfactant in the form of a plurality of relatively small slugs of surfactant fluid, and alternatingly injecting similarly small pore volume slugs of fluid comprising fresh water, e.g. salinities less than 10,000 parts per million and preferably less than 1000 parts per million total dissolved solids. The surfactant fluid comprises water containing at least one surfactant and up to 5.0 volume percent hydrocarbon, said hydrocarbon optionally containing an oil soluble silicone compound dissolved therein. The total pore volume of surfactant-containing fluid injected is ordinarily from 0.01 to 1.00 and preferably from 0.20 to 0.50 pore volumes. This total amount of surfactant fluid is injected in from 2 to 15 and preferably from 3 to 6 separate discrete slugs. Each slug of surfactant fluid is followed by injecting a quantity of fresh water. The volume of each fresh water slug is ordinarily from 0.5 to 5.0 and preferably 1 to 2 times the volume of the preceding surfactant fluid slug.