Aug-2024

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

Article Summary

The emergence of the hydrogen economy as part of the global drive to reduce greenhouse gas emissions has 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 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 natural hydrogen at concentrations greater than 10% (Zgonnik, 2020). The discovery has led to worldwide exploration and production activities, a few of which are summarised below. Most of these projects are at an early stage, which entails a high degree of uncertainty:

• Africa – Mali: Gas analysis data from a pioneer well and geochemical data from additional exploratory wells has confirmed the presence of an extensive hydrogen reservoir in the Bourakébougou field in Mali. The first well started production in 2014 and is producing 5 Mt/a (Prinzhofer & Cacas-Stentz, 2023).

• Australia – South Australia: In the 1920s and 1930s, oil exploration activity in South Australia found gas reservoirs rich in hydrogen. More recently, 35 permits have been granted for exploratory drilling for natural hydrogen (Alcimed, 2024). In 2023, test drilling in exploratory wells found gas with concentrations of up to 86% natural hydrogen and 6.8% helium, also a valuable substance (Gold Hydrogen, 2023). Then, in 2024, hydrogen at a purity of up to 95.8% was confirmed in the Ramsay 2 well (GoldHydrogen, 2024).

• Europe: Several European countries have geological formations associated with natural hydrogen. In France, the second phase of an exploration project, Regallor II, was initiated in 2024, with the goal of evaluating the size and potential for exploitation of a natural hydrogen reservoir in the coal basin in the Lorraine region of France. Reported estimates for the size of the Lorraine reservoir vary from 46 Mt of natural hydrogen (Meillaud & King, 2023) to as much as 250 Mt (Waltham, 2024; Bakx, 2024).

• North America – Canada: Much of Canada is covered with the type of rocks associated with the formation of natural hydrogen. The Geological Survey of Canada began building a database of potential deposits in 2022. While mapping will take several years, the process has prioritised several sites for detailed exploration in Northern Ontario and Quebec (Sejourne, et al., 2024), and test drilling in Northern Ontario is planned to start in 2024 (Bakx, 2024).

• North America – USA: The USGS is developing a global resource model for natural hydrogen, using analogues such as natural gas to help develop the scientific understanding of the subsurface behaviour of hydrogen. This model was used to predict the mean volume of hydrogen globally of 5.5 trillion tonnes. However, the USGS scientists note that most of this hydrogen is probably inaccessible, as it is either too deep or too far offshore or in accumulations too small for exploitation (Ellis & Gelman, 2023). Even then, there may be sufficient hydrogen that is economically accessible to constitute a primary energy source.

As elsewhere, the USGS is mapping the regions in the US most likely to contain natural hydrogen. One area of interest stretches along most of the Atlantic Coast, while a second area is in central US, including parts of the Great Plains and Upper Midwest (Ellis & Gelman, 2023).

An example workflow for the exploration process is shown in Figure 1.

Natural hydrogen as a renewable resource
The USGS considers that some of the gas in natural hydrogen fields may be renewable, given the rapid rate of hydrogen generation via water reduction. Some researchers have proposed that reservoirs, traps, and seals may not even be necessary to produce hydrogen. It may be possible to tap into rocks that are generating hydrogen or have hydrogen migrating through them to produce the hydrogen gas as it is being generated.

Other scientists propose that hot water could be injected into iron-rich rocks that are not currently generating hydrogen to stimulate generation (Ellis & Gelman, 2023). In the context of the move away from carbon emissions as part of the energy transition, such opportunities are exciting and merit significant research and development. At the same time, it should be noted that serpentisation is not a catalytic process (Zgonnik, 2020).