A comparative overview of geological formations for underground hydrogen storage: An innovative approach for energy storage

The large-scale deployment of hydrogen as an energy carrier is fundamentally constrained by the absence of robust, cost-effective storage solutions capable of managing seasonal and geographical variability in supply and demand. Geological Underground hydrogen storage (UHS) in salt caverns, depleted hydrocarbon reservoirs, saline aquifers, coal and basalt offers a technically promising and scalable solution. By analysing the advantages and challenges linked to these geological formations, the current review bridges essential knowledge gaps regarding hydrogen storage in subsurface formations. Key highlights include distinctive features of salt caverns, which offer low permeability, high structural strength and consequently less potential for leakage. In contrast, while depleted hydrocarbon reservoirs take advantage of existing infrastructure, they require extensive characterization during operation to ensure reservoir integrity and prevent gas leaks. Based upon the technology readiness level (TRL), basalt and coal are categorized as the least mature prospects for hydrogen storage and thus hold significant research potential for the future. Comparison of geological formations based on levelized cost of storage (LCOS) by qualitative ranking suggests that the LCOS of depleted oil and gas reservoirs is lowest, attributed to lower capital expenditure (CAPEX) from pre-existing infrastructure, followed by salt caverns, with saline aquifers having the highest LCOS due to the high requirement of cushion gas. Major formation-specific gaps and challenges include leakage, geochemical reactivity, microbial activity, and flow instability. These findings advance the understanding of UHS, aiding the development of the hydrogen economy to meet decarbonization goals and energy security.