IMMISCIBLE MICROEMULSION FLOODING.

Abstract

Economical microemulsion flooding inevitably involves microemulsion phases that are immiscible with water, oil, or both. Oil recovery is largely affected by displacement efficiency in the immiscible regime. Therefore, it is pertinent to study this immiscible aspect in relation to variables that affect phase behavior and interfacial tension between phases. This is accomplished through core flooding experiments wherein microemulsions immiscible with oil and/or water are injected to achieve enhanced oil recovery. One advantage of such an immiscible microemulsion flood is that surfactant concentration can be small and slug size large, thereby reducing deleterious effects of reservoir heterogeneity; a disadvantage is that the temporary high oil recovery accompanying locally miscible displacement before slug breakdown is reduced. Final oil saturation remaining after lower, middle-, and upper-phase microemulsion floods is studied as a function of salinity, cosolvent, temperature, and surfactant structure; and results are related to interfacial tension, phase behavior, and solubilization parameters. A conclusion is that immiscible microemulsion flooding is an attractive alternative to conventional microemulsion processes. Oil recovery obtained from microemulsion slugs is correlated with capillary number based on what is called the controlling interfacial tension. Physically, this means the least effective of the displacement processes at the slug front or rear determines the flood outcome. Finally, a screening procedure is developed that is useful for either immiscible or conventional microemulsion floods and that can reduce the number of core floods required to estimate oil recovery potential for a candidate microemulsion system.