Ugo Geymond’s PhD

Objectives of society’s decarbonation have brought H₂ under lights and the place of natural H₂ in the energetic mix of tomorrow is promising. Nonetheless, many questions are not resolved yet notably concerning the mechanisms involved in the generation of this resource.

Firstly discovered during the 1970’s at mid-oceanic ridges (Welhan & Craig, 1979), H₂ emissions are now observed in continental domain too, even more in the older regions: the Precambrian cratons. Due to its accessibility and the large number of emissions already discovered worldwide, natural H₂ in continental areas now stand as a field of research of prime interest.

Despite all the observations of H₂ leakage that have been observed at the surface during the past years (Larin and al., 2015 ; Zgonnik and al., 2015 ; Prinzhofer and al., 2019), the mechanisms leading to this generation at depth are still poorly constrained. In the literature many processes are proposed (Truche and al., 2020 et references therein), among: Reduction of water coupled with oxidation of Fe(II) contained in iron rich lithologies such as the serpentinization process in oceanic domain; Radiolysis of water triggered by energetic rays emitted during radioactive decay of U, Th, K in enriched continental lithologies; Degassing of magmas; Reaction of water with surface radicals during the fracturing of silicate rocks; Dehydrogenetation of clay minerals; Reaction of water with FeS to form FeS₂ + H₂; Or bacterial activity.

This PhD conducted in collaboration IPGP-UPPA-IFPen aims to explore the generation of H₂ in continental domain during Fe(II)-bearing minerals alteration. Promising sites will be investigated in Australia, where iron rich lithologies are numerous in the basement (ultrabasic rocks, BIF, etc)  and located directly below circular depressions notifying H₂ emissions (Moretti et al., 2021b, Frery et al., 2021).

Identification of H₂ sources and sampling during field work, associated with laboratory experiments and thermodynamic calculations will permit to: (1) Precise H₂ generation mechanisms implied as well as their kinetics; (2) Quantify H₂ fluxes that are emitted and evaluate the reel potential of this resource depending on the lithologies.