Method for using foams to improve alkaline flooding oil recovery

Abstract

An alkaline flooding oil recovery process is enhanced by injection of aqueous solutions of foam-forming surfactant and gases, or pre-formed foams, either ahead of or behind conventional alkaline slugs. In a preferred embodiment, a slug of an aqueous solution containing an alkaline agent followed by a driving fluid is injected into the formation that displaces oil through the relative high permeability zones of the formation and oil is recovered via the production well. Thereafter, a slug of an aqueous solution of a foam-forming surfactant is coinjected into the formation with a gas creating a foam when the gas mixes with the foam-forming surfactant in the aqueous solution. The foam created from the aqueous surfactant and gas will go preferentially into the formation zones of relatively high permeability and low oil saturation substantially plugging these zones. Thereafter, a slug of an aqueous solution containing an alkaline agent is injected followed by a driving fluid that displaces the aqueous solution containing an alkaline agent and oil through the less permeable zones of the formation toward the production well and oil is recovered from the formation via the production well. This process improves volumetric sweep efficiency and/or reduces effective mobility ratio of released oil and displacing fluids thereby enhancing displacement of oil to the production well and total oil recovery.