A preliminary review of risks in underground hydrogen storage

Underground hydrogen storage (UHS) is a promising solution for integrating hydrogen into the energy mix and ensuring a reliable and flexible energy supply. This work is part of ongoing research project Hydrogen UnderGround (HUG), funded by Business Finland, which aims at building the basis for large-scale hydrogen storage concept for the Finnish hydrogen business and technology ecosystem. The objective of this preliminary review is to gain a better understanding on the risks and uncertainties associated with UHS, especially concerning applicability to lined rock caverns (LRC). A lined rock cavern is a constructed underground storage facility, characterized by steel, polymer or concrete impermeable lining, designed to hold gases like hydrogen at high pressures. LRC is considered a feasible option for the Finnish conditions, due to lack of suitable natural geological formations. Other types of underground hydrogen storages may vary significantly in their geological and storage set-up, including aquifer, depleted oil/gas reservoir, rock/mining caves and salt caverns. The initial review comprised 60 articles, published between 2005-2024. The main risks in different types of storages were linked to technical factors, such as sealing and leakage, cavern integrity, geochemical, geomechanical, microbiological, hydrodynamic, or surface facility risks. Only one recent study mentioned economic and environmental risks, including social license to operate. Regarding LRC, a key non-technical risk identified was lack of experience with these caverns, which could be linked to competences and learning as human and organizational factors. This finding is in line also with results from other studies, which indicate that social factors are often insufficiently addressed in sustainable development reviews. The results highlighted the need for a holistic view on different risks for UHS, specifically emphasizing the uncertainties of technical system failure modes and deficiencies in understanding the role of non-technical factors, such as human, organizational and societal factors.