Surface wettability of sandstone and shale: Implication for CO2 storage

Reservoir wettability is an important factor controlling the CO2 geosequestration. In this study, temperature pressure and salinity effects were implemented to analyze the CO2 wettability alteration of the sandstone and shale reservoir. Previous studies on CO2 sequestration were mostly from the point of view of caprock wettability. This research is from the point of view of caprock and reservoir wettability, considers the sandstone and shale interbeded situation, which is less studied. Research results show that the contact angle of CO2/sandstone and CO2/shale decreases with pressure, which indicates that the reservoir is more CO2-wet in high pressure. In addition, the contact angle was not related to the temperature. Thirdly, the sandstones show strong hydrophilicity that has little relation with liquid salinity under standard temperature and pressure. Compared with sandstones, the hydrophilicity of the shales is weak. The CO2 wettability of shales increase with the salinity, due to the reason that shales have higher clay content and better oil saturation than the sandstones. Tests predict that low-pressure sandstone is suitable for the caprocks, high-pressure-low-temperature sandstone with better oil saturation, high-pressure-high-temperature sandstone with poor oil saturation, and low-temperature-high-pressure shale are ideal for CO2 storage.