Underground hydrogen storage: A review of technological developments, challenges, and opportunities

Hydrogen energy (HE) is a promising solution for large-scale energy storage, particularly for integrating intermittent renewable energy sources into the global energy system. A key enabler of this transition is underground hydrogen storage (UHS), which has the potential to store hydrogen (H2) at scale; however, its deployment remains a critical challenge due to technical, operational, and engineering complexities. In response to these challenges, this review provides a comprehensive analysis of UHS technologies, focusing on their feasibility, performance, and associated obstacles. The review considers the unique physicochemical properties of H2—such as density, viscosity, diffusion, solubility, and adsorption capacity—and their effects on subsurface storage. It then evaluates the feasibility of repurposing various geological formations for UHS, including depleted gas/oil reservoirs, salt caverns, aquifers, and abandoned coal mines. For each formation, the associated risks, uncertainties, and drilling and completion technologies are assessed, emphasizing the challenges specific to each environment. To ensure effective storage, fundamental trapping mechanisms—structural, residual, solubility, and mineral trapping—are analyzed, and their performance is compared across different geological settings. Technical factors influencing UHS performance are identified including petrophysical characterization, wettability effects, cushion gas requirements, and the impacts of H2 injection and production cycles. Key challenges associated with UHS, including caprock sealing, fault stability, reservoir leakage, wellbore integrity, geochemical and microbial reactions, geomechanical effects, unstable fluid displacements, microleakage, and drilling complexities, are also discussed. By identifying knowledge gaps and proposing targeted research directions, this review provides a structured framework for researchers, practitioners, and policymakers involved in the design and implementation of UHS systems.