Process for extracting extensively emulsion-free oil from a subterranean reservoir

Abstract

A process for extracting extensively emulsion-free oil from a subterranean deposit, the formation water of which has a medium or high total salinity and has a relatively low alkaline earth metal ion concentration, comprising injecting into an injection well therein a 1-20% strength aqueous tenside solution or dispersion in formation water of a mixture of 10-90% of carboxymethylated ethoxylates of the formula R--(OCH.sub.2 CH.sub.2).sub.n --OCH.sub.2 --COOM and 90-10% of ethoxylates of the formula R--(OCH.sub.2 CH.sub.2).sub.n --OH, wherein R is a linear or branched hydrocarbon aliphatic group of 4-20 carbon atoms or an alkylphenyl group of 1-14 carbon atoms in the alkyl group, n is 3-15, and M is an alkali or alkaline earth metal ion or ammonium, wherein alkaline earth metal ions are contained in the tenside solution or dispersion in such a concentration that the phase inversion temperature of the system:crude oil/formation water/tenside solution or dispersion, lies at most 10.degree. C. above the deposit temperature.

Dependencies are inferred from the claim text.