Static and Dynamic Exposure of Sandstone to a Hydrogen-Brine System: Geomechanical Alterations

Underground Hydrogen Storage (UHS) in saline aquifers and depleted gas reservoirs is a promising approach for large-scale energy storage; however, several challenges, including geomechanical challenges, must be addressed before widespread implementation. Hydrogen/brine-reservoir rock interactions, combined with cyclic stress conditions from hydrogen storage and withdrawal, may affect the geomechanical properties of the reservoir rock and its surroundings. It is essential to comprehensively assess the potential impact of hydrogen/brine-rock interactions on the geomechanical integrity of reservoir rock. In this study, we used two types of sandstone: quartz-rich (Red Felser) and clay-rich (Yellow Felser). These sandstones were subjected to two different exposure conditions, namely dynamic and static exposure, at high pressure and temperature. The quartz-rich sandstone was used for dynamic exposure, while the clay-rich sandstone was used for static exposure. The dynamic exposure is conducted using a core flood test under 100 bar, 80°C, for two months, while the static exposure is performed in an autoclave under 150 bar, 100°C, for six months. After exposure, triaxial cyclic laboratory experiments were conducted on both exposed (hydrogen-brine) and non-exposed (brine-only) samples at different confining pressures (10, 20, and 30 MPa). Additionally, eight stress cycles were applied in the linear regime (below the brittle yield point) before loading the sample to failure. The frequency, amplitude, and stress conditions of the cycles were adjusted for each confining pressure based on the brittle yield point. The results from dynamic exposure (hydrogen/brine-Red Felser sandstone) indicate minor changes in final strength and total inelastic deformation. However, alterations in the failure envelope (internal friction angle and cohesion) were negligible, and no changes were observed in Young’s modulus. The results from static exposure (Yellow Felser sandstone) suggest that six months of exposure had no impact on the failure envelope, elastic properties, total inelastic deformation, and acoustic characteristics. Our findings indicate that the interaction between hydrogen/brine and clay-rich and quartz-rich sandstones has a negligible effect on their geomechanical properties.