Pore-to-reservoir scale coupled thermal–hydraulic–mechanical–chemical–biological process benchmarking for underground hydrogen storage in porous reservoirs

Underground hydrogen storage (UHS) in porous reservoirs is governed by coupled multiphase flow, heat transfer, poromechanical stress redistribution, geochemical partitioning, and microbially mediated hydrogen consumption. A thermo–hydro–mechanical–chemical–biological (THMCB) benchmarking framework is developed and tested using an illustrative Ketzin-referenced case. The objective is to provide a consistent basis for nondimensionalization, process screening, pore-to-reservoir upscaling, and simulator verification. The main contribution is the integration of established THMCB equations within one scale-consistent benchmarking workflow. A thermodynamically consistent reservoir-scale THMCB model is formulated. It is used to analyze cyclic operation using hydraulic and thermal penetration behavior together with control-volume dissolution–consumption dynamics. The numerical results for repeated operating cycles use a 15-state control-volume ODE system. In the Ketzin-referenced benchmark, the imposed flow range remains Darcy–capillary dominated, hydraulic perturbations penetrate the reservoir thickness more rapidly than thermal oscillations, and gas–liquid hydrogen mass transfer is fast relative to the cycle time (–). The broad Forchheimer-coefficient sweep also identifies a non-Darcy near-well sector. Biogeochemical sweeps indicate sulfate-reduction dominance under the adopted chemical and microbial assumptions. The 50-year benchmark compares the characteristic length and time scales of gas–liquid hydrogen mass transfer, reaction, heat transport, poroelastic response, and periodic convergence. The 50-year calculation reports hydrogen return, reaction loss, and cycle-end repeatability using molar amounts per unit pore volume. These values are benchmark outputs and do not predict UHS performance at Ketzin. The model provides analytical tests for model simplification, calibration, and verification in porous-reservoir UHS.