Native Hydrogen generation in Granitic Geothermal reservoirs of the Upper Rhine Graben

WALLENTIN ANNA; MURRAY JESICA; LEMARCHAND DAMIEN; FRITZ BERTRAND; LUCAS YANN; BORDMANN VINCENT; SCHMITTBUHL JEAN

Pau

Workshop; Colloque Annuel du GdR CNRS HydroGEMM 2023; 2023

Université de Pau et des Pays de l'Adour

Over recent years, understanding reactions for natural hydrogen (H2) generation and the prospects offinding natural H2 occurrences have become of great interest. This is motivated by the importantrole of H2 as either an energy vector or a zero-carbon source of energy for the energy transition. Inthe field of Geothermal Energy, the co-production of georesources and potentially natural H2 fromdeep groundwater opened new perspectives for the deep geothermal sector as well. Previousresearch on the hydrothermal context of the Upper Rhine Graben suggests favorable conditions fornatural H2 generation through the alteration of Fe(II)-rich minerals in the granitic reservoirs [1].Therefore, the aim of this research is to further explore natural H2 generation associated to water-rock interactions on these geothermal systems. For that, three main aspects will be addressed bylaboratory work, geochemical modeling, and surface gas monitoring: i) alteration of Fe(II)-richminerals in the granite at different temperatures of the reservoir (130 – 200 ºC) and increasingpressures of CO2; ii) presence of fresh mineral surfaces with potential for Fe(II) oxidation and H2generation (using 6Li/7Li isotopes); iii) occurrence of subsurface H2 emanations. The context of theUpper Rhine Graben brings an opportunity to better understand natural H2 generation in graniticgeothermal reservoirs and to improve the current knowledge on H2 generation from water-rockreactions in the context of non-ultramafic rocks.