The Hydrogen System in the Subsurface: Implications for Natural Hydrogen Exploration

Abstract

Abstract In the context of global efforts to achieve carbon neutrality, Hydrogen (H2) has emerged as a key solution for reducing greenhouse gases emission. However, current methods of hydrogen production, such as thermochemical and electrochemical processes like electrolysis, methane reforming and pyrolysis, are generally expensive and suffer from issues including intensive carbon dioxide emission and high electricity consumption etc. (Ishaq et al. 2022; Younas et al. 2022). In fact, hydrogen gas can naturally occur in the subsurface which has been manifested by numerous hydrogen seepages found across the world (cf. Zgonnik 2020 and the references therein). Notably, a significant discovery of natural hydrogen was made accidently during drilling a water well (Bougou-1) in Mali in 1987. Subsequent exploration in the vicinity of Bougou-1 confirmed the existence of an active hydrogen system in the area (Prinzhofer et al. 2018), highlighting the possibility of commercial hydrogen accumulation in the subsurface. Moreover, there is a growing consensus that natural hydrogen could be an important alternative for hydrogen production (Zgonnik 2020). In recent years, extensive exploration activities and scientific research focusing on natural hydrogen occurrences, generation mechanisms, and accumulation processes have been conducted, particularly, in Africa (Moretti et al. 2022; Prinzhofer et al. 2018), Australia (Boreham et al. 2021; Frery et al. 2021; Leila eta al. 2022; Rezaee, 2021), Europe (Combaudon et al. 2022; Larin et al. 2015; Lefeuvre et al. 2022; Leila et al. 2021), Brazil (Moretti et al. 2021; Prinzhofer et al. 2019), and the USA (Guélard et al. 2017; Zgonnik et al. 2015). Geological investigations indicate that natural hydrogen is dominantly found on Precambrian cratons, ophiolite belts and mid-oceanic ridges (Rigollet and Prinzhofer, 2022). It occurs as gas leakages on the surface or is associated with other gases in the conventional and unconventional gas plays (Milkov 2022).