MOBILIZATION OF WATERFLOOD RESIDUAL OIL BY MISCIBLE FLUIDS.

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.