Oil recovery process

Abstract

A process for recovering oil from an oil-bearing subterranean reservoir penetrated by at least one injection well and at least one production well which comprises the steps of: (1) injecting into the oil-bearing subterranean reservoir through the injection well a first injecting fluid consisting essentially of (a) 1% to 30% by weight of an internal olefin sulfonate having 10 to 26 carbon atoms and a disulfonate content of 20% by weight or less, (b) 0.1% to 20% by weight of a cosurfactant, and (c) a brine; (2) injecting, as a second injecting fluid, an aqueous polymer solution having a viscosity higher than that of the first injecting fluid into the oil-bearing subterranean reservoir; and (3) recovering oil replaced with the first and second injecting fluids through the production well. This process can recover oil from subterranean reservoirs at a high oil recovery efficiency without destroying a micro-emulsion during sweeping in the subterranean reservoir even when the salt concentration of the formation water is widely changed.

Dependencies are inferred from the claim text.