Is abiotic hydrogen generation possible from the granitic basement in the Soultz-sous-Forêts Enhanced Geothermal System (Rhine Graben, France)? A hydro-geochemical modeling approach

CLÉMENT ALAIN; MURRAY JESICA; FRITZ BERTRAND; BORDMANN VINCENT; SCHMITTBUHL JEAN; JEAN-MARC FLEURY

Barcelona

Congreso; Goldschmidt 2019; 2019

H2 generation in natural reservoirs has recently promotedimportant researches in Earth Sciences stimulated by thechallenge of energy transition with possible alternatives tofossil fuel energy sources .Spontaneous H2 generation in natural geological systemshas been described in the context of serpentinization ofmafic and ultra-mafic rocks. In these systems the formationof H2 in fluid-rock interactions is due to the oxidation ofFe(II) bearing minerals and the often called reduction of H2O,which corresponds to the reduction of protons. Weinvestigate a way for abiotic H2 generation from the biotiterichgranite constituing the deep geothermal reservoir of theSoultz-sous-Forêts Enhanced Geothermal System.We applied the coupled transport and reaction modelKIRMAT to show that hydrogen production is possibleunder certain redox conditions in the fluids (low Eh, Tbetween 165 and 200°C) and hydrothermal alteration ofbiotite as a source of Fe2+, which oxidizes to Fe3+ andprecipitates into magnetite, while protons H+ are reduced intohydrogen H2. Looking for such favorable conditions is achallenge for future research.