Mobilization of Waterflood Residual Oil by Miscible Fluids

Abstract

Summary A study was conducted to determine how residual oil left by a waterflood is mobilized by miscible or low-interfacial-tension (IFT) fluids. Crude oils were used in the oil-displacement experiments with cores and sandpacks. In most previous investigations, refined oils were used. The residual crude oil was distinguished from injected oils by tagging of one or the other with olefins—hydrocarbons that are not present in crude oils but are easily and quantitatively distinguishable by analytical chromatographic techniques. The study shows that residual crude oil left by a waterflood is more accessible to an injected miscible fluid than is a residual refined oil, presumably through crude-oil-wetted surfaces of the rock. The results of laboratory coreflood displacements of residual or mobile refined oils (decane, soltrol, mineral oil, etc.) are not representative of reservoir formations containing indigenous crude oil. The displacement of residual crude oil by solvent is more efficient than displacement of refined oil by that solvent. Also, the displacement of residual oil by an oil or solvent at favorable mobility ratio occurs as a bank of oil production at a high flowing oil saturation approaching one minus the immobile water saturation. This saturation in a given porous medium at oil breakthrough depends on the viscosity of the residual oil.