Underground hydrogen storage: a review

Large-scale underground storage of hydrogen is expected to play a key role in the energy transition and in near future renewable energy systems. Despite this potential, experience in underground hydrogen storage remains limited. This work critically reviews the most important elements of this important technology, including hydrogen properties and their importance for subsurface operations, sources for hydrogen, and historical hydrogen storage operations, to set the state of the art. The cyclical nature of hydrogen storage operations will produce pressure and stress changes within the reservoir that could affect the integrity of the well, the reservoir, the caprock and the entire storage complex. To minimize geomechanical leakage risks and optimize the storage operation it is crucial to understand the pressure and stress history of the storage site, to optimize well locations to manage pressure, and to identify the reservoir-specific cushion gas-to-working gas ratio. Finally, the major scientific and operational challenges required to ensure the safe and efficient deployment of underground hydrogen storage at a large scale are here outlined.