article · Hydrogen
Storing green hydrogen underground is vital for deploying renewable energy at scale, but confining small, highly mobile hydrogen molecules for decades presents major technical hurdles. Containment performance varies across geological formations, including salt caverns, deep aquifers, depleted reservoirs, lined rock caverns and repurposed abandoned mines. While salt formations benefit from viscoplastic, self-healing properties that assist confinement, the interfaces between salt and cement, as well as general well infrastructure, remain vulnerable. Across all underground storage options, well integrity represents the primary risk factor for hydrogen leakage. Potential escape pathways include diffusion, advection, microcracking, cement degradation and complex hydrogen-material interactions. Geological storage also contends with geomechanical shifts, microbial reactions and regulatory challenges. Integrating hydrogen storage with carbon capture, utilisation and storage offers potential synergies, but overall success depends on targeted monitoring priorities, clear design criteria and further research into storage tightness.
Large-scale renewable energy systems require safe, long-term energy storage to balance supply and demand. Green hydrogen can provide this capacity if stored underground in massive quantities. However, because hydrogen molecules easily escape through minuscule defects and degrade materials, identifying leakage pathways and improving well integrity are essential steps toward preventing environmental hazards and ensuring the safe operation of future clean energy infrastructure.
This review provides design criteria, risk assessments and monitoring priorities for energy operators, engineers and regulators developing underground hydrogen storage facilities. The work is at an early review stage, intended to underpin future experimental and numerical research. While practical applications include repurposing depleted gas fields, salt caverns or abandoned mines, commercial-scale deployment requires resolving critical well-sealing vulnerabilities and establishing robust containment verification protocols.
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Underground storage of green hydrogen is a strategic enabler of large-scale renewable deployment, but its feasibility rests on a hard problem: keeping a small, highly mobile molecule confined underground for decades without safety or environmental risk. This critical review examines the containment mechanisms of hydrogen across underground storage types, focusing on geological barriers, well integrity and sealing materials. We evaluate the containment capabilities of salt cavities, deep aquifers and depleted reservoirs, with particular attention to the viscoplastic, self-healing properties of salt that promote confinement, and to the vulnerabilities of well infrastructure and salt–cement interfaces. Emerging alternatives, including lined rock caverns and repurposed abandoned mines, are assessed alongside their distinct operating configurations and use cases. Leakage mechanisms including diffusion, advection, microcracking, cement degradation and hydrogen–material interactions are analysed alongside geomechanical modelling, microbial activity, monitoring strategies, regulatory frameworks, and techno-economic and environmental considerations, including the integration of carbon capture, utilisation and storage (CCUS) with underground hydrogen storage. Well integrity emerges as the dominant risk factor across storage types. The review concludes with design criteria, monitoring priorities and research needs to guide the safe, sustainable deployment of underground hydrogen storage, providing a scientific foundation for future numerical and experimental work on storage tightness.
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DOI: 10.3390/hydrogen7030116
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