A Review of Hydrogen Storage in Geological Formations

This review presents a thorough analysis of the technical, geological, and economic aspects of Underground Hydrogen Storage (UHS), positioning it as a key enabler for large-scale deployment of clean hydrogen supply chains. As global hydrogen demand increases particularly in traditional sectors such as refining and ammonia production the development of safe, seasonal, and scalable storage systems becomes essential to support renewable-based energy infrastructures. Geological hydrogen storage is identified as the most viable solution due to its advantages in volumetric energy density, intrinsic safety, and the availability of suitable subsurface structures such as salt caverns, depleted hydrocarbon reservoirs, and deep aquifers. Techno-economic analyses show that UHS is considerably more cost-effective and technically feasible for large volumes compared to surface-based storage methods. The review synthesizes real-world experiences from the UK, USA, and Austria, where field-scale pilot projects demonstrated up to 82% recovery of injected hydrogen with no significant degradation in reservoir integrity. The paper also highlights challenges related to microbial activity, particularly in porous formations with residual hydrocarbons or brine, where biological methanation or hydrogen loss could occur. A comparative analysis of hydrogen’s physical properties versus methane is included, focusing on density, viscosity, interfacial tension, solubility, and diffusivity, and how these influence hydrogen behavior in porous geologic media. Additionally, the role of cushion gas (e.g., CO₂, N₂, CH₄) is evaluated for its contribution to maintaining reservoir pressure and enhancing extraction performance. The gas selection is shown to significantly impact chemical compatibility, environmental risk, and operational efficiency. In conclusion, this review underscores that the successful deployment of UHS requires a multi-scale understanding of hydrogen dynamics in subsurface formations, supported by robust experimental validation and numerical modeling, to ensure safe, efficient, and climate-resilient storage operations over the long term.