Natural hydrogen can help achieve a clean, secure and affordable energy future, but its generation, migration and accumulation in the subsurface is not well constrained. Only few case-studies exist but hydrogen-dominated natural gas has been reported in some wells in Australia. CSIRO has a role to play to build the critical subsurface knowledge to accelerate access to and production of natural hydrogen resources.
Hydrogen-bearing fluids and hydrogen free gas were encountered in fluid inclusions in fracture-fill cements in granites of the Hiltaba Suite, South Australia. The fluid inclusions were identified in cores in a geothermal exploration well drilled close to the Olympic Dam iron oxide-copper-gold (IOCG) ore deposits. Petrographic analyses identified a possible source of hydrogen in the hydrothermal alteration of plagioclase that also resulted in generation of porosity at the microscale. In-situ oxygen isotope values in quartz fracture-fill cements indicate an input of meteoric water in the system, in addition to the crustal component (local oxygen remobilization or hydrothermal fluids).
Additionally, noble gases were measured from bulk crushed samples at the CSIRO noble gas facility using a Helix MC high resolution noble gas mass spectrometer. Neon isotopes measured on whole granite grains (1-2 mm) showed an increasing radiogenic contribution with depth indicative of very old fluid components that display long-term isolation.
The integrated outcomes of this research on rocks that have been reported as a possible source of natural hydrogen help us define the mechanisms of fluid-rock interactions and fluid charge history that has potential for predicting natural hydrogen occurrence as an energy source.