The effect of crude oil composition on wettability alteration at smooth quartz surfaces is compared to alteration of the wetting properties of sandstones. In both types of study, after adsorption at elevated temperature, the mineral surface was washed or flushed with a solvent to leave an adsorbed organic film. Cores prepared in this way have mixed wettability and are referred to as MXW-F cores. Wetting studies were then performed using an aqueous phase and mineral oil as the oleic phase. Previously reported contact angle measurements at smooth quartz surfaces for ten crude oils showed that asphaltic crudes gave stable advancing and receding contact angles whereas for paraffinic oils wetting was unstable. Instability was evidenced by decrease in contact angle hysteresis for repeated measurements of advancing and receding contact angles.
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