Research Of Rock Wettability Alteration Mechanisms Concerning Low Interfacial Tension System

Quartz was used as typically surface of sandstone reservoir in this paper, compositions of oil which induced wettability alteration of quartz surface was studied and quartz surface with different wettability was obtained. The mechanisms of wettability alteration induced by different surfactant system were studied. Optimized surfactant systems with different ability of interfacial tension reduction and wettability alteration were selected. Static washing oil and oil displacement experiment ware conducted to study the synergistic effect of interfacial tension reduction of oil water interface and wettability alteration of rock surface on oil recovery. The data of experiments show that the advancing angle of formation water on water wet quartz surface is about 10.03°. When the quartz was soaked by oil acid toluene solution, the advancing angle changes to about 71.40°; if the quartz was treated by asphaltene toluene solution or formation oil, the advancing angle is about 93.51°. Quartz was aged by 20% heptane-oil mixture, the advancing angle changes to about 138.6°. Analysis of IR spectra indicates that asphaltene interact with hydroxyls on quartz surface by polar reaction, and asphaltene can absorbed on quartz surface with ion bonding. Surfactant can alters the wettability of quartz surface at very low concentration, anionic surfactant has small influence of the wettability of water wet quartz surface and can changes the intermediate or oil wet quartz surface to strong water wet. The static washing oil and oil displacement experiment results are all suggest that lower interfacial tension of oil water interface or change the rock wettability to water wet only can not get the highest oil recovery ratio except to performing the synergistic effect of interfacial tension reduction and rock surface wettability alteration.