Cycle-Dependent Thm Assessment of Deep Underground Hydrogen Storage Using a Matlab-Based Numerical Framework

Underground hydrogen storage (UHS) in deep geological formations is increasingly recognized as a promising solution for large-scale and long-duration energy storage. However, its long-term operational reliability depends on preserving the mechanical integrity of the host rock–caprock system during repeated hydrogen injection and withdrawal cycles. Under such conditions, coupled thermo–hydro–mechanical (THM) processes, together with simplified chemo-mechanical effects represented through porosity–permeability evolution, govern stress redistribution, deformation, and damage accumulation within the subsurface formation. This study presents a cycle-resolved numerical investigation of UHS using a fully coupled THM framework implemented in MATLAB to evaluate the progressive geomechanical response under cyclic operation. The simulations reveal pronounced effective stress-path hysteresis, irreversible strain accumulation, and localized damage initiation concentrated around the storage formation and lithological interfaces. During peak injection, vertical stress increases by approximately 20–25%, while cyclic pore-pressure fluctuations of 5–6 MPa promote progressive mechanical degradation over successive loading cycles. The coupled analysis further indicates that damage-induced permeability may increase by nearly one order of magnitude in localized regions, highlighting the strong interaction between mechanical degradation and hydraulic transport. Although thermoelastic effects generated by gas compression and expansion are smaller than pressure-driven responses, they accelerate early-stage damage evolution during repeated cycling. Overall, the findings demonstrate that the long-term integrity and containment performance of underground hydrogen storage systems cannot be reliably evaluated using single-cycle or peak-pressure criteria alone, but require comprehensive assessment of cumulative coupled THM processes under sustained cyclic operation. The proposed framework provides a physically consistent computational basis for evaluating long-term storage integrity and supporting the design of resilient underground hydrogen storage facilities.