Oil recovery process using a tapered surfactant concentration slug

Abstract From the Canadian patent

A, TAPERED SURFACTANT CONCENTRATION SLUG (D#74,012-FB), ABSTRACT OF THE DISCLOSURE A process for recovering oil from a subterranean reservoir in which a surfactant slug injected into the formation via an injection well is passed through the formation and oil is recovered via a production well penetrating the formation. In this process a tapered surfactant concentration slug is employed in which the surfactant concentration is increased, either incrementally or gradually, during the slug injection time. The slug can be a simple aqueous solution of the surfactant a hydrocarbon-in-, water emulsion containing the surfactant or an aqueous solution of a polymer containing the surfactant.