Evaluation of Reservoir Wettability and its Effect on Oil Recovery.

This project has three main goals. The first is to achieve improved understanding of the surface and interfacial properties of crude oils and their interactions with mineral surfaces. The second goal is to apply the results of surface studies to improved predictions of oil production in laboratory experiments. Finally, we aim to use the results of this research to recommend ways to improve oil recovery by waterflooding. In order to achieve these goals, the mechanisms of wetting alteration must be explained. We propose a methodology for studying those mechanisms on mineral surfaces, then applying the results to prediction and observation of wetting alteration in porous media. Improved understanding of the underlying mechanisms will show when and how wettability in the reservoir can be altered and under what circumstances that alteration would be beneficial in terms of increased production of oil. Crude Oil/Brine/Solid Interactions The interactions between crude oils, brines, and solid surfaces have been studied using a variety of core materials as well as in two-dimensional micromodels of interconnecting pores and throats. In the work reported this quarter, these same interactions have been applied to create mixed-wet conditions in a very simple model porous material, namely square glass tubes which have the advantage of permitting dual occupancy by both wetting and nonwetting phases simultaneously. The interactions between crude oil samples from Prudhoe Bay have been studied on a variety of surfaces. Figure 1 outlines the regions of stable and unstable brine compositions with A-93, a sample from Prudhoe Bay, and glass surfaces. A brine with pH 8 and 1 M concentration of NaCl produces a stable water film between glass and A-93 crude oil. If the brine has pH 4 and 0.01M NaCl, thin films of water are unstable and oil contacts the glass. Between these extremes is a wide band of brine compositions for which film stability is conditional