b'FeatureHydrogen explorationHydrogen exploration: The next big thing?Naturally occurring H 2 -fertile geological settings include regions of serpentinised mafic rocks (eg, ophiolites) and regions tapped by faults that act as conduits for mantle-derived hydrogen (eg, Ellouz et al, 2003; Ulrich et al., 2020; Lefeuvre et al, 2021) In these examples, the process of serpentinisation of mafic rocks produces fluids which are highly enriched in molecular hydrogen The liberation of hydrogen from serpentinite by percolating groundwater is analogous to the generation of oil and gas from kerogen in the hydrocarbon kitchen Recent measurements of gas seepages in the ophiolitic rocks of New Caledonia into ultrabasic spring water (pH ~10-11) show that the gases are H 2 -N 2 -CH 4mixtures with H 2Bhavik Harish Lodhiacontents between 1234% (Deville etal. 2021, Patriat et al Department of Minerals and Energy Resource Engineering2022) Recent investigations of natural hydrogen seeps in the University of New South Wales SydneyWestern Pyrenees, Spain, found that major thrust faults may act b.lodhia@unsw.edu.au as conduits for hydrogen produced by the serpentinisation of mafic mantle rocks at depth (Lefeuvre etal. 2021) The ability The world is going through strange times Whilst the globalfor hydrogen to migrate along faults is not surprising, but race towards carbon Net-Zero continues, 2022 has seenrepresents the important step of migration Furthermore, the hydrocarbon commodity prices peak Hydrogen has emergedprospect of meteoric waters percolating through naturally as a potential saviour to the worlds energy crisis, withfractured serpentinised rocks raises obvious parallels to increasing resources being dedicated to developing hydrogenhydraulic fracturing The final step in the hydrogen kitchen is technology, infrastructure, and storage capacity However,the existence of a trap that can hold hydrogen on timescales the production of hydrogen from water is both costly andsuitable for extraction by humans Clearly, this is different to a extremely energy intensive The concept of natural hydrogentrap capable of holding stable hydrocarbons in the traditional exploration remains beyond conventional thinking amongsthydrocarbon kitchenmany geoscientists A key stumbling block remains in finding sources of environmentally friendly, or green hydrogen ThisThe storage of gaseous hydrogen in salt caverns is already used begs the question: can natural hydrogen be explored for andon an industrial scale (Andersson and Grnkvist 2019) As is exploited? Recent measurements of H 2 -fertile geological regionswell known, salt deposition occurs as water evaporates and indicate high natural hydrogen generation at the present daythick accumulations characterise salt basins across the world in regions that contain altered basic igneous rocks In thisSubsurface salt bodies may be significant in size and be 10-100s article, I explore the possibility of applying the well-establishedkm long and several kilometres high Hence, it is possible that salt hydrocarbon kitchen concept to the exploration of hydrogen asbodies within the vicinity of buried mafic rocks may be charged a commercially exploitable resource by hydrogen produced by serpentinisation and delivered by faults It is exciting that the geological and stratigraphic Old fashioned cooking accumulation of hydrogen, ie trap, may be achieved by the Traditional thinking by geoscientists exploring for oil and gas is dominated by the well-established concept of the petroleum kitchen In a successful petroleum kitchen, an organic-rich source rock such as shale, expels hydrocarbons as it is buried and experiences increased pressures and temperatures, ie, cooked Buoyant hydrocarbons migrate along carrier beds until they reach an impermeable barrier and accumulate in structural or stratigraphic traps These traps are targets for hydrocarbon exploration These processes occur over geological timescales and are predicted in a variety of ways, including using basin modelling However, most geologists and geoscientists across both academia and industry share the preconception that naturally occurring hydrogen cannot accumulate in geological formations orFigure 1.Conceptual model for possible fluid-rock interactions at the New remain stable for geologically significant periods This is becauseCaledonia ophiolite. Sp = Serpentenite, SRTs = Subduction-related terranes hydrogen, as the lightest element, is highly mobile (e.g., Diabot Terrane at New Caledonia). Interaction between percolating meteoric waters and serpentinised mafic rocks at base of the fossil subduction A new kitchen zone are known to produce H2-rich fluids (Ulrich et al, 2020; Patriat et al, 2022). Movement along natural fractures within serpentinites or faults may Several lines of recent research indicate that the percolation ofprovide migration pathways to natural hydrogen seeps at the surface. Modified meteoric fluids along faults characteristic to fossil arccontinentfrom Ulrich et al, 2020. A salt diapir is displayed for illustrative purposes only, which may act as a store for naturally produced hydrogen (e.g. Andersson and collision orogens (eg, New Caledonia) and other hydrogen- Grnkvist, 2019; Lefeuvre et al., 2021). Salt structures have been identified in the rich terranes may play an important role in the formation ofNew Caledonia Basin (e.g., Auzende et al., 2000), thus illustrating the interesting hydrogen-rich fluids (Dugamin, Truche and Donz, 2019; Ulrichpossibility of a meteoric fluidserpentiniteevaporite hydrogen kitchen in et al, 2020; Patriat et al, 2022) (Figure 1) similar geological settings around the world.39 PREVIEW OCTOBER 2022'