In-situ wettability alteration of organic-rich shale caprock in hydrogen with cushion gas: Implications for hydrogen geo-storage

XR Yu and SD Rao and LY Zhang and YX Li and CW Liu and M Yang and ZX Chen, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 103, 75-86 (2025).

DOI: 10.1016/j.ijhydene.2025.01.062

Underground hydrogen storage (UHS) is a promising technology that can effectively store hydrogen with large capacity and low cost. As important parameters, water contact angle and rock wettability can describe mobility and capillary trapping of reservoir fluids, further affecting sealing efficiency, hydrogen injection, and production strategies in UHS. These two parameters in hydrogen-organic shale systems as a function of temperature, pressure, and mixed gas composition have been investigated by molecular simulations. Results show that the water contact angle decreases with increasing temperature, and the temperature effect on the wettability alteration is not apparent at high hydrogen pressure. The hydrogen-shale system becomes less water- wet as the hydrogen pressure increases. However, it can stay water-wet when the pressure is 40 MPa, indicating that capillary trapping still contributes to hydrogen storage at high pressure. A theoretical parameter K is proposed to compare the gas tendency to wet the solid for CO2/CH4-hydrogen mixtures. When the CO2 fraction increases to 25 %, the system wettability changes from strongly water-wet to gas-wet, which reduces the sealing capacity of shale. A neutrally wet state can be achieved when the CH4 fraction is 75 %, ensuring stable extraction efficiency and a low possibility of gas leakage.

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