This paper presents a definitive account of the effect of wettability on oil recovery from Berea sandstone based on the results of more than 50 slow-rate laboratory waterfloods. Closely reproducible wettability conditions and waterflood recoveries were obtained with wettability, depending on the crude oil, brine composition, aging temperature, and initial water saturation. Maximum oil recovery by waterflooding was obtained at very weakly water-wet conditions from shortly after breakthrough up to discontinuation of the test at 20 PV of water injected. In most of the tests, coproduction of oil and water continued long after breakthrough.
Numerous reports of experimental work relating to the role of wettability in various aspects of oil recovery have been published. Several recent reviews are available. All point out the diverse conclusions regarding the optimum wetting condition for oil recovery by waterflooding. This probably results from problems in obtaining wettability control and characterization and differences in the nature of the systems used in evaluating wettability effects. In several investigations, wettability of cores and other porous media was altered by chemical treatment, usually with an organochlorosilane. A disadvantage of this technique is the inconsistency in wetting condition with time because of hydrolysis and desorption of weakly adsorbed molecules. Aside from concerns about the artificial nature of such systems, no generally accepted standard procedures exist for generating a spectrum of wettability conditions by chemical treatment.