Hydrogen Storage Induces Earlier Leakage and Greater Surface Deformation Compared to Compressed Air and Viscous Gases

Underground hydrogen storage (UHS) in porous media reservoirs is increasingly being considered as a means to balance the intermittency of renewable energy systems. However, the geomechanical risks associated with the cyclic injection and production of hydrogen remain underexplored compared to compressed air energy storage (CAES) and the storage of more viscous gases, such as CO₂ and CH₄. This study employs coupled hydro-mechanical numerical simulations of a sandstone reservoir bounded by shale caprock and underburden, intersected by a steeply dipping fault, and overlain by an upper aquifer. We compare deformation, fluid migration, and leakage risks between hydrogen and compressed air under identical cyclic injection scenarios using an integrated workflow that combines a stress-dependent Barton-Bandis caprock fracturing model with a Coulomb friction-based fault permeability evolution model.

Our results reveal that both hydrogen and compressed air follow similar failure sequences: injection-induced pressure buildup triggers caprock failure, followed by gas migration into the caprock and subsequent fault activation. However, critical differences emerge in timing and magnitude. In UHS, leakage into the caprock and overlying aquifer initiates much earlier in the injection cycle compared to CAES. Furthermore, hydrogen consistently results in substantially higher cumulative leakage volumes and generates larger magnitudes of surface uplift and subsidence. This amplified surface deformation is driven by stronger pressure perturbations and a more vertically extensive gas plume, a direct consequence of hydrogen’s high mobility.

These findings suggest that hydrogen compromises reservoir geomechanical integrity faster than compressed air. Since CAES fluids are already less viscous than CH₄ or CO₂, the containment challenges identified here for hydrogen are more severe than other underground gas storage systems. Our findings reveal that site-selection and integrity criteria for CAES, CO₂, or CH₄ storage are inadequate for UHS. UHS requires revised caprock permeability thresholds and enhanced leak detection strategies (such as real-time fault and surface monitoring) to ensure safer operations and infrastructure repurposing from depleted fields.