The Great Hydrogen Hideaway

The growing global demand for energy, coupled with the urgent need to reduce greenhouse gas emissions, has accelerated the transition toward low-carbon energy systems (Ahmed et al., 2023; Lin et al., 2023). Hydrogen (H2) has emerged as a key energy carrier in this transition due to its high energy density, clean end-use, and compatibility with renewable production pathways such as water electrolysis, biomass conversion, and thermochemical processes (Bartoli et al., 2025; Cormos, 2023; Tang et al., 2023). Despite its advantages, the widespread deployment of H2 is constrained by the challenge of safe, economical, and large-scale storage, as conventional surface storage methods, including compressed tanks and liquefaction, are limited in capacity, efficiency, and long-term feasibility (Fang et al., 2025; Glenn et al., 2023; Krebsz et al., 2025). Underground hydrogen storage (UHS) has therefore gained increasing attention as a practical solution for large-scale and seasonal hydrogen storage, leveraging the substantial capacity of geological formations (Abreu et al., 2023; Hemme et al., 2018). Potential storage media include salt caverns, depleted oil and gas reservoirs, and deep saline aquifers, with salt caverns currently representing the only commercially deployed option for pure hydrogen storage due to their low permeability and operational maturity (Alms et al., 2023; Heinemann et al., 2021; Okoroafor et al., 2024; Qian et al., 2025; Shi et al., 2025). However, saline aquifers and depleted reservoirs are increasingly being investigated because of their vast availability, despite the additional complexity associated with fluid-fluid and fluid-rock interactions under subsurface conditions (Abdelaal et al., 2025; Huang et al., 2025; Lou et al., 2024). Figure 1 depicts geological formations mostly favorable for UHS. Figure 1: Schematic illustration of UHS options in geological formations.