Analytical equations to estimate hydrogen storage efficiency factor and storage capacity in saline aquifers

Saline aquifers are potential storage sites for CO2, CH4, and H2. While extensive research has been conducted on CO2 storage efficiency in saline aquifers, our understanding of hydrogen storage efficiency remains limited. This study compares the efficiency of CO2 and hydrogen storage in saline aquifers and investigates whether the CO2 efficiency factor is analogous to the hydrogen efficiency factor. We evaluated both closed and open aquifer systems, conducting over 160 numerical simulations that considered porosity, permeability, reservoir pressure and fracture pressure variations. The result shows that CO2 and H2 storage efficiency factors have a strong correlation in closed systems. However, in open systems, the relationship is unclear, suggesting that CO2 efficiency cannot represent hydrogen storage efficiency. The study determines hydrogen storage efficiency estimates in different aquifers, resulting in values that range from 0.1 % to 4.2 %. Ultimately, we propose analytical equations to quantify the saline aquifer's efficiency factor and storage capacity for underground hydrogen storage.