Hydrogen storage in geological porous media: Solubility, mineral trapping, H2S generation and salt precipitation

Hydrogen as a significant energy vector plays an important role in the decarbonization of heavy industry. However, the intermittency and sessional availability of renewable energy sources, as well as the demand for energy at different times and places, require a medium-to long-term storage technology. Underground storage of hydrogen in depleted gas reservoirs and saline aquifers could be a good option given their storage capacity and availability in different geological settings. However, these geological porous media may suffer from many operational, geological, and geochemical complications. This paper attempts to evaluate the geochemical in-teractions posed by the injection of hydrogen into porous media. The results obtained from a series of ther-modynamic and kinetic geochemical modeling calibrated against experimental data show that dissolution of carbonates, anhydrate and halite can occur over time, leading to precipitation of calcite, formation of H2S and long-term closure of the pore structure due to scale formation. The reduction of pyrite to pyrrhotite is likely to occur at a temperature above 90 degrees C, which may enhance the formation of H2S in the absence of microbial ac-tivity. The formation of scale (halite) is a long-term process that only starts after 10 years of operation due to the slow dissolution of halite in porous media. However, during hydrogen injection, salt diffusion, the formation of a dry-out zone and the phenomenon of salting out occur, depending on the salinity and temperature of the for-mation water. The results of this study can help to better understand and select geological porous media for large-scale hydrogen storage.