Geochemical evaluation of subsurface hydrogen-brine-mineral interactions and hydrogen loss

Naturally occurring and stored hydrogen in subsurface pores in rocks can undergo abiotic reactions driven by interactions with minerals, formation water, and coexisting gases. These reactions may result in hydrogen loss, altering reservoir injectivity, mineral structure, and gas composition. To systematically evaluate these geochemical processes, this study integrates equilibrium modeling to assess the long-term thermodynamic stability of hydrogen and kinetic batch modeling to capture time-dependent hydrogen-mineral reactions. Within this modeling framework, key properties such as hydrogen solubility, pH variations, mineral dissolution and precipitation, and hydrogen loss mechanisms are analyzed under various thermodynamic conditions relevant to both hydrogen storage and natural hydrogen occurrences. The results demonstrate that hydrogen solubility in brine increases with pressure and temperature and decreases with salinity due to salting-out effects. In pure mineral systems, most silicate and carbonate minerals remain largely unaltered. However, sulfate-bearing minerals exhibit significant reactivity under hydrogen-bearing brine conditions, with anhydrite undergoing complete dissolution, resulting in H 2 S formation and additional hydrogen consumption associated with pyrite-pyrrhotite transformation. In mixed mineral systems, distinct responses emerge for sandstone and dolomitic limestone, with limited reactivity in silicate-dominated sandstone and enhanced carbonate and sulfide mineral reactions in dolomitic limestone, resulting in further hydrogen consumption. These findings clarify the key abiotic geochemical pathways governing hydrogen stability and retention in subsurface hydrogen storage and along hydrogen’s migration pathway when it is naturally occurring.