Reactive-transport screening of H2S/souring tendency during underground hydrogen storage

Hydrogen sulfide generation is a potential gas-quality concern during underground hydrogen storage, especially in sulfate- and Fe-bearing reservoirs. This study develops a staged PHREEQC–PHREEQCRM framework to screen H 2 S/souring tendency under H 2 -rich conditions using equilibrium geochemical calculations and simplified one-dimensional reactive transport. The framework evaluates sulfate availability, pH-dependent sulfide speciation, Fe-mineral buffering, lithology, temperature, H 2 fugacity, and cushion-gas composition. Results are interpreted as comparative screening outcomes rather than field-scale predictions of H 2 S generation or produced-gas H 2 S concentration. Under imposed equilibrium conditions, sulfate availability alone did not define souring tendency; reduced sulfur accumulation occurred only under H 2 -controlled reducing equilibrium. pH controlled HS − /H 2 S(aq) partitioning, with lower pH favoring aqueous H 2 S(aq). Fe-bearing mineralogy showed mineral-dependent effects on dissolved sulfide, while the mixed Fe-mineral case produced explicit pyrite formation and solid-phase sulfur uptake. One-dimensional reactive-transport screening further suggested lower dissolved reduced sulfur and H 2 S(aq) in Fe-buffered systems than in the unbuffered reference case.