Adsorption-Induced Deformation in Microporous Kerogen by Hydrogen and Methane: Implications for Underground Hydrogen Storage

Accurately assessing the adsorption and diffusion behaviors of H2, CH4, and their mixtures are essential for estimating underground hydrogen storage (UHS). This understanding is critical for the safe and efficient storage of H2 in depleted shale gas reservoirs. Although H2 adsorption in kerogen has been extensively studied, adsorption-induced swelling remains unexplored in UHS. In this study, we investigate adsorption mechanisms using Lagrangian and Eulerian approaches and analyze diffusion in kerogen through molecular simulations. Our results reveal that in the presence of cushion gases like CH4, which exhibit stronger adsorption than H2, neglecting kerogen deformation can lead to an underestimation of storage capacity by approximately 40%. Furthermore, increasing pressure makes H2 adsorption behavior deviate from the consistent swelling trend that is observed with CH4, with kerogen either swelling or contracting depending on the pore size. Simulations also predict that H2 self-diffusion coefficient in porous kerogen is 1 order of magnitude higher than CH4. These findings highlight the importance of incorporating kerogen flexibility into the modeling of UHS involving multiple gas species to improve the accuracy and safety of H2 storage operations in shale reservoirs.