Evolution of Wetting Alteration by Adsorption From Crude Oil

Summary Crude oils are complex mixtures of organic molecules, some of which can adsorb onto high-energy surfaces, altering mineral surface wettability. In cores, the extent of wetting alteration varies with oil and brine compositions and saturations as well as with aging time and temperature. Previous studies on flat surfaces have demonstrated rapid interaction between oil components and solid surfaces that can vary with the composition of the intervening brine phase. This study is designed to investigate interactions that occur after initial oil/solid contact. Wettability alteration is assessed by measurement of contact angles between pure fluids after removal of bulk crude oil. The influences of aging time, temperature, and fluid compositions have been considered. Adsorption appears to proceed in two stages. Initial exposure of wet surfaces to oil produces weakly water-wet conditions. Longer aging may produce oil-wet surfaces or, in some cases, a return to more water-wet conditions. This second stage of the adsorption process may continue for days or even weeks and is influenced by temperature and fluid compositions. Desorption of crude oil components can occur when a treated surface is re-exposed to brine.