Underground hydrogen storage: A critical assessment of fluid-fluid and fluid-rock interactions

Underground hydrogen storage (UHS) is the injection of hydrogen into the geologic porous medium for subsequent withdrawal and reuse during off-peak periods to contribute to the energy mix. Recently, UHS has gained prodigious attention due to its efficiency for the storage of hydrogen on a large scale. Nonetheless, an adequate understanding of the storage process is required for efficient and safe monitoring and to preserve reservoir integrity. Herein, the hydrodynamics of injected hydrogen (H2) gas, reservoir fluids, and reservoir rock systems are reviewed. Moreover, critical factors inherent to the reservoir (such as temperature, pressure, salinity, and rock mineralogy) that affect the UHS process are elucidated. Based on the available literature, the interplay of H2 solubility, interfacial tension, wettability, adsorption, and diffusion properties influence the geologic storage process. Overall, this review provides extensive insight into fluid-fluid and fluid-rock interactions and their effect on underground hydrogen storage process. Future research should focus on optimizing the process parameters to improve storage and withdrawal efficiency, thus guarantee energy security.