Underground hydrogen storage (UHS) has been proposed as one option for storage of excess energy from renewable sources. Depleted gas reservoirs appear suitable, but at the same time, they may be environments with potentially high microbial abundances and activities. Hydrogen (H2) is one of the most energetic substrates in such environments, and many microorganisms are able to oxidize H2, potentially leading to loss of H2 or other unwanted reactions like production of, e.g., H2S, clogging, or corrosion. This study addressed the potential of H2 consumption by naturally abundant microorganisms in formation fluid from a gas field at near in situ pressure and temperature conditions. Microbial H2 consumption was evident at ambient and 100 bar and tolerated pressure variations reflecting cycles of H2 storage. Temperature strongly influenced the activity with higher activity at 30 °C but lower activity at 60 °C. The activity was sulfate-dependent, and sulfide was produced. The microbial community composition changed during H2 consumption with an increase in sulfate-reducing prokaryotes (SRP). Thus, the presence of an SRP-containing, H2-consuming microbial community with activity at UHS-relevant pressure and temperature conditions was shown and should be taken into account when planning UHS at this and other sites.
Keywords: formation fluid; high pressure; hydrogen H2; microbial activity; porous reservoir rock; sulfate reduction; underground storage.