Hongwen Zhao

 Introduction Energy transition from fossil fuels to renewable energy and hydrogen energy is believed to be one of key solutions to cope with decarbonization. Under this circumstance, natural hydrogen exploration (gold hydrogen) and Hydrogen production with subsurface simulation (orange hydrogen) gains more attentions due to its low cost and low carbon footprints as compared to manufactured hydrogen. However, there is no methodologies for hydrogen resource potential evaluation in place. This paper proposes a graph-based approach with constrains from mineralogy of source rocks and environmental conditions of serpentinization. The method can serve as a quick tool to do natural hydrogen potential estimation for any given Fe-rich rock bodies. 2. Methods Natural hydrogen generation has been attributed to a variety of generation mechanisms in which the hydration of Fe-rich ultramafic/mafic minerals (serpentinization) is considered as a major one responsible for hydrogen emissions found across the global. This method is to develop a series of templates quantitatively depicting the relationships among hydrogen gas yields, the content of Fe-bearing minerals in the source rocks, and the degree of serpentinization. For a given targeting area, the potential hydrogen generation can be evaluated based on 3 inputs:1) the volume of Fe-rich rocks which can be estimated on regional geological map and multiphysical data. 2) the content of Fe-bearing mineral, and 3) the degree of serpentinization can be inferred from XRD and petrography of the rock samples. 3. Results Serpentinization is a complex metamorphic process of ferromagnesian minerals characterized by the hydration and the oxidation of reduced iron species resulting in H2 generation. Geochemical modeling shows that various reaction pathways of serpentinization may take place, such as. 6Fe2SiO4 (fayalite) + 7H2O → 3Fe3Si2O5(OH)4 (chrysotile) + Fe3O4 (magnetite) + H2 (1) 3Fe2SiO4 (fayalite) + 2H2O → 2Fe3O4 (magnetite) + 3SiO2 + 2H2 (2) The controlling factors include mineral composition, temperature, pH values, water/rock ratio, reactive surface area and water compositions. Given that a) a rock body has a volume of 1.88E+08 cubic meters, b) composited dominantly of olivine with 10% of fayalite; 3) the degree of serpentinization varies between 0 to 100%. Two templates are created based on equation (1) and (2). The estimated H2 generation can be read on two graphs. For the lower case (equation 1), the potentially generated H2 range from 0 to 8.32E07 kg while the rock body is serpentinized between 0 to 100%. For an upper case, 0 to 3.7E08 kg of H2 would be generated while the serpentinization proceeded from 0 to 100%. 4. Conclusions This paper proposed an innovative tool to estimate the H2 generation potential of Fe-rich rocks during serpentinization, which provides critical information for the techno-economic analysis of gold hydrogen and orange hydrogen projects.

Co-auteur : Ernest Jones, Hasnol Hady Ismail