Technical challenges and opportunities of hydrogen storage: A comprehensive review on different types of underground storage

As the global energy structure rapidly transforms to clean energy, underground hydrogen storage(UHS) technology is critical in achieving large-scale, seasonal energy storage. This paper reviews hydrogen storage media, including salt caverns, depleted oil and gas reservoirs, aquifers, and abandoned coal mines, and evaluates their advantages, disadvantages, and practical feasibility. The specific needs and challenges faced by UHS are highlighted by comparing the physical properties of H2, CH4, and CO2. Subsequently, the technical challenges encountered in the hydrogen storage process are discussed from four aspects: caprock sealing, reservoir geochemical reactions, microbial activity, and wellbore integrity. In addition, the fluid dynamics interaction between hydrogen, cushion gases (such as CH4 and CO2), brine, and rock is deeply analyzed, with particular attention to the effects of interfacial tension, wettability, and capillary pressure on hydrogen storage performance. In summary, the study on hydrogen's dissolution and diffusion characteristics in micropores and nanopores is still insufficient. Geochemical reaction and microbial activity are the main factors of hydrogen loss. The problems of hydrogen causing corrosion, hydrogen embrittlement, and failure of wellbore systems have also not been systematically evaluated. Therefore, future focus should be on fluid dynamics and geomechanics to better understand and address these challenges.