Role of Immobile Phase Saturations in Tertiary Oil Recovery

Abstract

ABSTRACT The presence of an immobile phase – oil, water, or gas – can influence the performance of an oil recovery process, adversely under most conditions. Furthermore, the flood velocity exerts an additional effect on the role of the immobile phase. The paper discusses the effect of an immobile phase on dispersion in porous media. Specifically, solvent flooding is examined in the context of immobile oil, water, and gas phases. The phase saturations were reduced below the critical values to study an extended saturation range. Also tested was the effect of entrained polymer on dispersive mixing. Although the studies were primarily conducted in a miscible displacement framework, the results are examined in the context of other recovery methods as well, such as micellar and alkaline flooding. Solvent flooding of very viscous oils is also considered, wherein the dispersion behavior is controlled by the dissolution of an initially immobile oleic phase. The results obtained show that dispersion in a porous medium tends to decrease in the case of wetting immobile phase. The behavior is opposite if the immobile phase is nonwetting (oil or gas). For wetting phase saturations below the critical, the mixing coefficient first decreases then increases with an increase in saturation. The opposite behavior is observed in the case of nonwetting phase. In all cases the mixing coefficient is rate-dependent, the direction of change being governed by the type and magnitude of the immobile saturation. The practical implications of the above observations from the point of view of tertiary oil recovery processes are discussed.