Measurements Of Fractional Wettability Of Oil Fields' Rocks By The Nuclear Magnetic Relaxation Method

Abstract

Introduction The wettability of reservoir rocks is recognized as one of the major factors that determines their multiphase flow properties. Multiphase flow properties in turn govern reservoir performance. For this reason, the reservoir engineer is vitally interested in the wettability of reservoir rock. The production research scientist is interested in wettability because the solution of the problem of improving water flood recovery by use of surface-active additives may hinge on a detailed understanding of the wettability of reservoir rock. Early workers believed that all reservoir rocks were preferentially water wet. Continued study soon uncovered certain rocks which had flow properties that indicated that they were preferentially oil wet. Recent studies show that there is a spectrum of wettability. Some reservoir rocks have multiphase flow properties which indicate that they have an intermediate wettability. The differences in recovery observed among different reservoirs may, in part, be the result of small differences in wettability. Differences in wettability among reservoir rocks may be the result of differences in the friction of the total surface area that is preferentially oil wet and preferentially water wet. Nuclear magnetic relaxation measurements provide a method for determining the fraction of preferentially oil wet and preferentially water wet area in porous media. Measurements to be reported here were made on water saturated unconsolidated sand packs which were mixtures of preferentially oil wet and preferentially water wet sands. The resulting data show definitely that the fraction of each wettability in the sand pack can be determined by this nondestructive method of measurement.