Fully Coupled THM Modeling of Hydrogen Migration, Storage, and Recovery in Depleted Gas Reservoirs

Background & Motivation■ Net zero needs storage: hydrogen could supply about 13% of global final energy demand by 2050 in the IEA net-zero scenario, so safe, large-scale storage is essential.■ Underground storage in porous rock offers high capacity and low cost, but there is little large-scale operating experience.■ H₂ is the smallest molecule and highly penetrating, so its migration, mixing and recovery must be predicted, not assumed.■ Injection raises reservoir pressure and can deform the rock.Thermal-hydraulic (TH) models ignore this feedback.Why a fully coupled THM model? Reservoir pressurizationDeformation and stability issues Accurate reservoir pressure prediction THM = Thermal-Hydraulic-Mechanical Objective & NoveltyObjective: based on TOUGH2-CSM, develop a fully coupled THM model for hydrogen storage in depleted gas reservoirs, then use it to evaluate injection, shut-in and production behavior and to optimize operating strategies. What is new■ Stress effect: poroelastic deformation feeds back on pressure through stressdependent rock properties.■ Hydrogen-specific EOS: flash calculations for H₂O-CO₂-CH₄-H₂-N₂ mixtures.■ Strategy comparison: injection depth and cushion gas (CO₂, N₂) evaluated in one verified framework.