Toward a Fundamental Understanding of Geological Hydrogen Storage

Geological H-2 storage plays a central role to enable the successful transition to the renewable H-2 economy and achieve net-zero emission in the atmosphere. Depleted oil and gas reservoirs are already explored with extensive reservoir and operational data. However, residual hydrocarbons can mix with injected H-2 in the reservoirs. Furthermore, low density and high diffusivity of H-2 may establish H-2 leakage from the reservoirs via fault pathways. Interestingly, H-2 can be consumed by microorganisms, which results in pore-network precipitation, plugging, and partial permeability impairment. Therefore, stored H-2 may be lost (i)n the formations if the storage scenario is not planned cautiously. While salt caverns are safe and commercially proven geo-rock for H-2 storage, they have low-storage capacity compared to depleted gas reservoirs. Moreover, salt structures (e.g., domel, bedded) and microorganisms activities in the salt cavern are limiting factors, which can influence the storage process. Accordingly, we discuss challenges and future perspectives of hydrogen storage in different geological settings. We also highlight geographical limitations with diverse microbial communities and theoretical understanding of abiotic transformation (in terms of rock's minerals, i.e., mica and calcite) for geological H-2 storage. Regarding the fundamental behavior of H-2 in the geological settings, it is less soluble in formation water; therefore, it may achieve less solubility trapping compared to CO2 and CH4. Furthermore, H-2 gas could attain higher capillary entrance pressures in porous media over CH4 and CO2 due to higher interfacial tension. Additionally, the low viscosity of H-2 may facilitate its injection and production but H-2 may establish the secondary trapping and viscous fingering. Thus, this review documents a blend of key information for the amendment of subsurface H-2 storage at the industrial scale.

Automated summary

Geological H-2 storage plays a critical role in transitioning to a renewable hydrogen economy and achieving net-zero emissions. However, challenges such as H-2 leakage, microbial consumption, and storage capacity limitations exist.