EVOLUTION OF WETTING ALTERATION BY ADSORPTION FROM CRUDE-OIL

Crude oils are complex mixtures of organic molecules, some of which ca n adsorb onto high-energy surfaces, altering mineral surface wettabili ty. In cores, the extent of wetting alteration varies with oil and bri ne compositions and saturations as well as with aging time and tempera ture. Previous studies on flat surfaces have demonstrated rapid intera ction 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 be tween pure fluids after removal of bulk crude oil. The influences of a ging time, temperature, and fluid compositions have been considered. A dsorption appears to proceed in two stages. Initial exposure of wet su rfaces to oil produces weakly water-wet conditions. Longer aging may p roduce oil-wet surfaces or, in some cases, a return to more water-wet conditions. This second stage of the adsorption process may continue f or days or even weeks and is influenced by temperature and fluid compo sitions. Desorption of crude oil components can occur when a treated s urface is re-exposed to brine.