Effect of System Wettability on Oil Displacement By Micellar Flooding

Abstract

This paper studies the recovery of waterflood residual oil by micellar floods using laboratory oil- and water-wet cores. Excellent agreement is found between experiment and theory. The study also shows greater chemical costs and decreases in injectivity for oil-wet systems. Introduction The recovery of waterflood residual oil in laboratory water-wet porous media by a micellar or microemulsion solution has been discussed extensively. Many studies have defined the requirements (mobility control and capillary number) for effective oil displacement, discussed the relationship of micellar fluid design and oil recovery performance, reported the laboratory data for design of field tests, discussed the mechanisms of oil displacement, and investigated surfactant loss. With few exceptions, similar studies in oil-wet media have not been reported, although at least three pilot micellar floods have been conducted or planned in intermediate or oil-wet reservoirs. Although one might expect the requirements for oil displacement to be similar in water- and oil-wet media, there are fundamental differences in the recovery of oil, as demonstrated by waterflood performance and in the physical structure and distribution of the waterflood residual oil. In particular, the reduction of interfacial tension required for displacement of the wetting phase has been investigated only theoretically and experimentally in synthetic systerms. Only one study containing laboratory micellar flood data in oil-wet cores has been presented. This study discussed the micellar fluid design for a planned pilot test and compared the fluid's oil recovery pilot test and compared the fluid's oil recovery performance in water-wet cores with oil-wet. The chosen performance in water-wet cores with oil-wet. The chosen surfactant system required almost twice the slug size for strongly oil-wet media to achieve the tertiary oil recovery obtained with water-wet cores. Such a comparison has not been determined yet because the requirements for oil displacement and the displacement mechanisms are not the same in oil- and water-wet systems. In other words, a fluid that is optimal for water-wet porous media may not be optimal for oil-wet porous media. This study was undertaken to determine whether there are significant differencesin the requirements for oil displacement by a micellar fluid in oil- and water-wet cores, andbetween the oil displacement mechanisms of micellar fluids in oil- and water-wet cores. The results of seven continuous-injection, micellar slug tests with three different micellar fluids are presented and discussed. Theories are proposed to explain differences in the oil recovery performance between oil- and water-wet cores. The results of a series of small-slug tests (7 to 35 percent PV micellar fluid injected) also are discussed. percent PV micellar fluid injected) also are discussed. Their performance is explained in terms of the proposed theories. The implications on micellar fluid design, both in oil- and water-wet media, are brought out. Evidence of a chromatographic separation of a micellar fluid is presented also. presented also. Requirements for Oil Displacement Effective oil displacement by micellar flooding requires an increase in mobility control and capillary, number (mu u/ gamma). Mobility control is a function of relative permeability. The water- and oil-wet relative-permeability permeability. The water- and oil-wet relative-permeability curves used in this study are depicted in Fig. 1. JPT P. 52