The geomicrobiology of hydrogen storage in geological materials

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To rollout UK hydrogen storage in the subsurface, information is needed regarding the geological storage site itself and the hydrogen - microbe interactions that occur in these subsurface environments. Primarily in the UK, geological formations desired for hydrogen storage are caverns by dissolution (storage in salt deposits) or in porous media, such as aquifers and depleted oil and gas fields (DOGF). Subsurface microbial processes, chemical and mineralogical reactions between hydrogen and the rock material can produce unwanted by products (hydrogen sulphide, methane, bio clogging) leading to impurities in the returned gas or changes in cavern/reservoir heterogeneity. There are known microbes (e.g., methanogens, sulphur reducing bacteria, homoacetogens) that consume hydrogen as an energy source, but it is not clear how their colonies interact/compete with one another or the processes/mechanisms which dominate in the subsurface. Existing knowledge of subsurface microbial process is limited. For large scale underground hydrogen storage three areas are proposed: salt caverns, depleted oil and gas reservoirs and saline aquifers. Experimental work will be carried out to understand the hydrogen microbe interactions and their effects on the geochemical reactivity on reservoir mineralogy. Salt caverns currently act as storage for most of the hydrogen and a large proportion of natural gas globally. Either scaling up or converting natural gas stores to hydrogen is likely to happen as hydrogen usage expands. However, there are limited studies on how microbes in the salt caverns interact with the hydrogen gas. This is important as it could reduce both the yield and purity of hydrogen which could lead to post storage purification being required at additional costs. Porous media (DOGF and saline aquifers) are especially advantageous for green hydrogen where salt cavern storage is not easily accessible without large scale pipeline infrastructure, but subsurface reservoirs are nearby, (e.g., offshore wind to produce green hydrogen and straight to underground storage). Porous media offering huge volumes of hydrogen gas competed to salt caverns and an already existing pipeline network in the North Sea can be repurposed/refitted to deliver hydrogen. With ample information from the oil and gas industry in the North Sea, geology is already surveyed with known conditions of porosity and permeability, two factors hugely important for any type of porous media gas storage. Microorganisms will be determined through 16s rRNA sequencing conducted on Illumina MiSeq platform at the NU-OMICS sequencing service (Northumbria University). Petrographic analysis will be carried out before and after hydrogen microbial interaction experiments to determine if any mineralogical changes to the reservoir (e.g., mineral dissolution or precipitation). If time permits, potential geological storage sites be looked at across the UK, onshore and offshore. Specifically looking into Permian and Triassic Salt deposits and saline aquifers and DOGF on the UKCS.