Safety Aspects Related to the Underground Hydrogen Storage

The transition from fossil fuels to the renewable energies (wind, solar) is a key factor to face climate change and build a sustainable, reliable, and secure energy system. To balance the intermittent energy demand and supply affecting the renewable sources, the surplus of electrical energy may be converted in hydrogen and then storage in geological formations. While the risks associated to the natural gas storage in the sub-surface are well known from decades, those associated with hydrogen underground storage (UHS) are relatively underexplored. This paper presents an inventory of risks related to large H2-storage in depleted gas and oil fields, salt caverns and aquifers. Different issues such as integrity and durability of materials, H2 leakages and interaction with the reservoir, H2 uncontrolled outflow from the wellhead with potential combustion of air-hydrogen mixture (fire and explosion), soil subsidence and induced seismicity, are analyzed.