Hydrogen gas has an important role to play in a decarbonised economy, either as an energy vector or as a zero-carbon energy source.

LabEx G-eau-thermie Profonde researchers, in collaboration with TOTAL, have been investigating how H2 can be generated abiotically – that is, without an associated biological process – in the biotite-rich granite reservoir at Soultz-sous-Forêts.

Lead author, Jesica Murray, and colleagues  used a geochemical approach to simulate the hydrothermal alteration of granite between 130°C and 200°C, temperatures typically found in deep geothermal reservoirs. They found that in an open system – where fluids can enter and exist the geothermal reservoir – biotite alteration leads to hydrogen production. When biotite is allowed to alter completely, a reservoir like Soultz-sous-Forêts could produce up to 102 000 tons of hydrogen per cubic kilometer.

While further research is needed to understand how to optimise the alteration reaction and maximise hydrogen production, the authors found that injecting CO2 – a key greenhouse gas – into the reservoir could stimulate the alteration process.

These exciting results bring us closer to understanding how we can optimise reservoir productivity by coupling heat extraction with hydrogen production, for a more carbon-neutral energy future.

For more detailed  information, you can read the study in full in Applied Geochemistry (Open Access).