Stimulating Hydrogen Generation in Serpentinised Peridotite: Field-Scale Injection Experiments in Oman

Hydrogen is expected to play a central role in the global energy transition, yet most industrial hydrogen production remains associated with significant CO₂ emissions. Natural hydrogen generated during serpentinisation of ultramafic rocks offers a low-carbon alternative, but its distribution, generation rates, and recoverability remain poorly constrained. To date, most research has focused on identifying naturally occurring hydrogen systems. Here, we explore a complementary approach: testing whether hydrogen-producing reactions in ultramafic rocks can be engineered to achieve economic production through subsurface stimulation. We present results from the Rock Hydrogen Project, a field-scale pilot experiment conducted in serpentinised peridotite in Oman, a globally recognised natural laboratory for ultramafic-hosted fluid–rock interactions. The project investigates the feasibility of enhancing hydrogen generation through controlled water injection into fractured peridotite at almost 1km depth. Downhole geophysical logging was used to characterise fracture distributions, providing a structural framework for interpreting pressure and flow responses. Then, a large-volume water injection, followed by a pump-back phase was completed. During this test, pressure, flow, fluid chemistry, and resulting gas compositions were monitored. Hydrological data outlines injectivity and pressure evolution, while recovered fluids and gases were analysed for major and trace elements, noble gases and major gas compositions using gas chromatography and noble gas mass spectrometry. This integrated dataset captures the coupled hydrological and geochemical evolution of fluids during subsurface circulation and the influence of stress-dependent permeability. Recovered fluids show pronounced chemical modification relative to injected waters, including increased salinity, alkaline pH (up to ~11.5), increased gas concentrations and highly reducing conditions. Measured gas compositions are dominated by hydrogen and small amounts of methane. Together, these observations indicate rapid fluid-rock interaction during injection and recovery. Ongoing work aims to test whether such stimulation can drive the production of hydrogen in fractured peridotite at relatively low temperatures. Next steps include the continued development of fracture network models based on downhole data, continued integration of hydrological and geochemical observations, and the drilling of an additional borehole to establish an injection–production array to test optimal rate of fluid circulation for hydrogen production. These efforts aim to quantify net hydrogen generation rates, evaluate scalability, and improve understanding of the coupled processes governing stimulated hydrogen systems in ultramafic reservoirs.