Decarbonisation Technology - August 2024 Issue

Potential of natural hydrogen in the energy transition For energy-intensive industries looking to clean hydrogen as a means of decarbonisation, natural hydrogen can reduce uncertainty and cost

Himmat Singh Ex Scientist ‘G’ CSIR, Indian Institute of Petroleum and Advisor R&D, BPCL

T he emergence of the hydrogen invigorated interest in naturally occurring molecular hydrogen. Natural or geologic hydrogen is ubiquitous at low concentrations in the subsurface environment, while it can accumulate in higher concentrations when trapped in pockets deeper underground, similar to oil and natural gas. Geologists hypothesise that untapped reservoirs of natural hydrogen may be found globally, including in Africa, the Americas, Asia, Australia, Europe, and Russia. These are often, but not only, associated with depleted oil and gas reservoirs (Zgonnik, 2020) . This has led to an upturn in geological modelling to determine the volume of known reservoirs, as well as exploration activities to discover and assess the potential of new reservoirs. This research suggests that the Earth contains a greater amount of natural hydrogen than previously assumed. The US Geological Survey (USGS) estimates there may be as much as 5.5 trillion tonnes of hydrogen in underground economy as part of the global drive to reduce greenhouse gas emissions has reservoirs worldwide (Blain, 2024), (Ellis & Gelman, 2023) . The process for hydrogen generation via water reduction is rapid, implying that natural hydrogen could constitute a renewable, clean energy source (USGS, 2023). It also raises the prospect that abundant, renewable, natural hydrogen could be exploited at costs similar to that of natural gas when the cost of carbon emissions is considered. Formation of natural hydrogen Natural hydrogen is molecular hydrogen that

has been generated by a range of geological and biological processes at shallow level and deep subterranean levels. Of the many processes that generate hydrogen, two of the main ones are considered to be serpentisation and radiolysis (Zgonnik, 2020):  Serpentinisation: Mafic rocks and minerals are magnesium and iron silicates, such as olivine and pyroxene. These minerals are widespread components of the Earth’s lithosphere – the crust and mantle. When groundwater comes into contact with mafic minerals, the water is reduced to oxygen, which binds with the iron to form serpentites and hydrogen.  Radiolysis: Trace radioactive elements in rocks emit radiation that can split water into hydrogen and oxygen. This is believed to be the main mechanism for the production of the Earth’s oxygen over the geological timescale. In addition, streams of hydrogen from the Earth’s core or mantle may rise along tectonic plate boundaries and faults. Hydrogen is highly diffusive, so it travels quickly through faults and fractures. In shallower layers of rocks, microbes metabolise hydrogen to produce methane. At deeper levels, abiotic reactions can occur to form methane, water, and mineral compounds (USGS, 2023). A global search The prevalence of serpentinisation and radiolysis reactions in Mafic rocks from the Precambrian continental lithosphere, which covers 70% of the global continental crust surface area, suggests a global rather than regional potential for hydrogen evolution (Day, 2023). This has been confirmed by widespread discoveries of