Microbial risk assessment for underground hydrogen storage in porous rocks

Geological hydrogen storage, e.g. in depleted gas fields (DGF), can overcome imbalances between supply and demand in the renewable energy sector and facilitate the transition to a low carbon emissions society. A range of subsurface microorganisms utilise hydrogen, which may have important implications for hydrogen recovery, clogging and corrosion. We gathered temperature and salinity data for 75 DGF on the UK continental shelf and mapped their suitability for hydrogen storage in terms of the risk of adverse microbial effects, based on a novel collection of microbial growth constraints. Data on wind and solar operational capacities as well as offshore gas and condensate pipeline infrastructure were overlaid on the microbial risk categorization to optimize geographical centers of green hydrogen production, transport infrastructure and underground storage. We recommend storing hydrogen in 9 DGF that are at no microbial risk due to temperatures > 122 °C, or in the 35 low-risk DGF with temperatures > 90 °C. We recommend against utilising high-risk DGF with temperatures < 55 °C (9 DGF). Alignment with centers for renewable energy production and out-of-use pipelines suitable for repurposing to transport hydrogen suggests that no-risk and low-risk DGF in the Southern North Sea are the most suitable candidates for hydrogen storage. Our results advise site selection choices in geological hydrogen storage in the UK. Our methodology is applicable to any underground porous rock system globally.