Role of Methanogenesis and Sulfate Reduction in Lifetime Performance of Hydrogen Storage in Depleted Gas Reservoirs

Geological formations potentially provide suitable options for underground hydrogen storage (UHS). For seasonal operations of UHS, working gas capacity cannot coincide with the total amount of hydrogen stored in a geological formation where key aims include (i) maintaining reservoir pressure, and (ii) avoiding productions of cushion gas (e.g., CO2, CH4, N2) during withdrawal cycles. Otherwise, when considering long-term (or lifetime) UHS scenarios, the kinetics of the chemical reactions associated with mixtures of hydrogen with the fluids residing in the porous formation can evolve to attain equilibrium conditions. Here, we consider lifetime behavior of UHS scenarios and assess uncertainties associated with hydrogen losses due to its conversion into other chemical species. Given the time scales involved, we disregard kinetic behavior of hydrogen consuming reactions while evaluating the loss of underground stored hydrogen due to its conversion to other chemical products at reservoir thermodynamic equilibrium conditions. Our results are tied to (i) shallow, (ii) intermediate, and (iii) deep reservoirs. Our modeling study suggests that hydrogen losses at equilibrium conditions in shallow reservoirs (low temperature/pressure conditions) is around 5% more (on average) than the corresponding losses associated with deep reservoirs (high temperature/pressure conditions).