Influence of Supercritical CO <sub>2</sub> Exposure on Water Wettability of Marine and Continental Shale

Abstract

To investigate the influence of supercritical CO2 (ScCO2) exposure on water wettability of shale, a systematic contact angle experiments considering ScCO2 exposure time and pressure were conducted on shale samples collected from Sichuan Basin (marine) and Ordos Basin (continental), respectively. In addition, X-ray diffraction analysis and low-pressure N2 adsorption were performed to evaluate the variations of mineral compositions and pore structure of shale. Results indicate that the tested shale samples are both hydrophilic rocks, and the shale-water contact angles generally increased with increasing ScCO2 exposure time and pressure, which is primarily caused by the the decrease of clay minerals and carbonates in shale. The water wettability of shale weakened after ScCO2 exposure, indicating that the interaction between shale and water molecules decreased, which may reduce the resistance of water to flow in pores and fractures of shale. Accordingly, it can be inferred that the alteration of shale water wettability after ScCO2 injection is beneficial to the seepage of gas in shale pore channels, but may exist a negative influence on the stability of CO2 geological sequestration. This study provides a theoretical reference for CO2 sequestration and CO2-enhanced shale gas recovery (CS-ESGR).