Ensuring Safe Hydrogen Storage: Advanced Numerical Modelling of Caprock Integrity and Reservoir Geomechanics for Hydrogen Containment and Leakage Prevention

Abstract Underground hydrogen storage (UHS) is a key technology for large-scale, long-duration energy storage, supporting seasonal balancing of renewable generation and demand. Geological options such as saline aquifers, depleted reservoirs, and salt caverns offer significant capacity, yet cyclic injection and withdrawal can trigger complex hydro-mechanical responses that affect both performance and containment integrity. In this study, a fully coupled two-dimensional poromechanical model was developed to evaluate the stability of a homogeneous saline aquifer under repeated hydrogen cycling. The framework integrates a pressure equation, well representation, and Biot's poroelastic formulation with an explicit creep deformation component, enabling the simulation of pore pressure, stresses, volumetric strain, and property evolution. Flow simulations showed strongly localized pressure build-up and smooth radial dissipation, mirrored by the volumetric strain field. Laboratory observations further confirmed the temperature sensitivity of creep and the role of mineral heterogeneity in accelerating fracture nucleation. Single-cycle simulations revealed localized property changes near the injector, with permeability enhancement driven by elastic dilation, while two-cycle analyses demonstrated cumulative effects, including residual porosity and up to 27% permeability increase at the injector. Incorporating creep highlighted a ratcheting mechanism, whereby volumetric strain and permeability changes accumulated across cycles even under constant loading magnitudes. These results demonstrate the necessity of accounting for both time-dependent deformation and flow-mechanical coupling when evaluating UHS performance, as cyclic operations can induce progressive, spatially localized changes that influence injectivity and long-term containment.