Executive summary

What is natural hydrogen?

Hydrogen is widely used in the petrochemical industry and in fertiliser production. It gives off no carbon dioxide when burned, making it a promising replacement for fossil fuels and a method of storing renewable energy. Traditionally made from fossil fuels (eg methane), focus has shifted to producing ‘green hydrogen’ from the electrolysis of water powered by renewable energy. However, this process is energy intensive and requires a rapid expansion of renewable energy capacity. Considering this, alternative hydrogen sources that do not rely on fossil fuels are gaining interest. This includes ‘natural hydrogen’.

Natural hydrogen as defined in this report is hydrogen that occurs in rocks and soils in the Earth’s crust produced by geochemical and biological processes, without any human involvement. In this report we focus on natural hydrogen already present as hydrogen (H₂), as opposed to processes of stimulation or fracking to enhance hydrogen production from rocks (sometimes called stimulated geologic hydrogen). Hydrogen has long been known in the oil, gas and mining industries, and has been extensively studied around the world through studies of the deep subsurface microbial biosphere, but in terms of energy or economic potential has generally been treated as an unwanted byproduct and/or a risk factor.

Formation of natural hydrogen

There are two main natural mechanisms that are known to produce hydrogen:

• Serpentinisation and other chemical reactions between water and rocks rich in iron
• Radiolysis – the splitting of water molecules by naturally occurring and safe radiation within rocks containing uranium (U), thorium (Th) or potassium (K)

The types of rock which typically could produce hydrogen are quite common worldwide. However, production and preservation depend on factors such as the geology, water availability, temperature, gas migration pathways and the absence of microbial activity that might rapidly consume hydrogen – all of which are active areas of research. The use of surface phenomenon including hydrogen seeps and soil gas concentration monitoring as an exploration tool is under development, but it is important to consider the potential for false positives (eg hydrogen production from microbes, or drilling artifacts), and false negatives (eg due to microbial consumption of hydrogen diffusing from potential commercial accumulations at depth). Although large volcanic/hydrothermal sources of hydrogen exist around the world, these areas are usually not practical for commercial extraction. Indeed, coupling hydrogen data with noble gas tracers suggests there is little evidence to date to support claims of economic long-term renewable natural hydrogen sources of volcanic/ mantle origin.

The potential for natural hydrogen as a future energy source

There is currently not enough publicly available data to give an accurate figure for the potential volumes of natural hydrogen stored in specific subsurface trapped in reservoirs, but global flux estimates have been made for decades. Reviewing recent literature suggests that, excluding volcanic gas flux (as noted, unlikely to be a commercial target), continental geological hydrogen flux can be estimated to be <0.74 million tonnes H₂/year. Including volcanic gas flux yields a value of <1.74 million tonnes H₂/year. Based on hydrogen measurements, both estimates are significantly lower than some recently proposed values based on modelling. In all cases the estimates are substantive, all the more so if such hydrogen fluxes can accumulate in subsurface traps over long geological time scales. Discoveries of such significant accumulations of natural hydrogen in the continents, in traps that are sustained by hydrogen fluxes of this magnitude, could be a game changer. Even capturing a small proportion for commercial use could enable natural hydrogen to play a significant role in the coming years.

Currently, natural hydrogen is only produced commercially at the Bourakébougou Field, a small site in Mali, which powers local energy needs. But exploration projects are currently underway around the globe, including but not limited to France, Spain, Australia, USA, Finland and Canada. The impact of these projects on local, regional or international energy markets is still uncertain and will depend on many factors such as the scale of the discovery, its location relative to potential markets and the purity of the hydrogen.

Initial targets for economic exploitation of hydrogen may be most favourable in regional concentrated industrial hubs co-located on the same geologic settings where hydrogen accumulations have most often been found (eg iron-rich or iron-magnesium rich rocks that are already the hubs for mining of gold, copper, nickel, diamonds or critical minerals). As storage/transport infrastructure for hydrogen of all forms (including green hydrogen) develop on a global scale, natural hydrogen hubs may form part of those larger networks and markets.

UK potential for natural hydrogen

The UK has developed a hydrogen strategy and is planning to use low-carbon hydrogen to replace fossil fuels in a variety of uses. The current plans focus on the generation of green hydrogen (defined above) and blue hydrogen (from fossil fuel but coupled with carbon capture utilisation and storage; CCUS). Like many other countries around the world, the UK does have some geological areas that may have the potential to accumulate significant quantities of natural hydrogen. This includes geologic settings with hydrogen generation potential from radiolysis (including granites, mafic and ultramafic rocks) as well as serpentinisation (mafic and ultramafic rock). For the United Kingdom no databases currently exist to evaluate occurrences of natural hydrogen, and no co-ordinated nationwide exploration has taken place. Available maps to date from other countries are often empirical, and as such are inherently prone to the ‘false negative’ problem ie locations with no hydrogen may be because hydrogen has not been looked for; or, because hydrogen has not been analysed for (as until recently hydrogen analysis was not part of routine gas analysis and reporting). Globally much effort is focusing on producing maps of hydrogen potential moving from empirical maps of reported occurrences to more predictive maps integrating mineralogy, lithology, structural and trapping features, transport pathways, and geophysical data.

Technologies and environmental impact of extracting natural hydrogen

It is generally understood that technology needed for natural hydrogen extraction will be similar to that for natural gas well exploration, exploitation and monitoring for leak detection, but with design adjustments for hydrogen’s unique properties. Extraction could involve drilling several deep production wells into the geological formation trapping the hydrogen, followed by purification and storage on the surface.

Natural hydrogen is often found co-located with other substances including methane (CH₄), carbon dioxide (CO₂), helium (He), nitrogen (N₂) and lithium (Li). While helium and lithium can make natural hydrogen extraction more commercially viable, other impurities such as carbon dioxide and methane might increase costs due to the need for separation and disposal.

Whilst natural hydrogen itself poses no more environmental hazards than hydrogen produced by other methods, its extraction will have different impacts on the environment, both above and below ground. Care will need to be taken to keep hydrogen leakage to a minimum and the impact of hydrogen exploration and exploitation on subsurface microbiology is not well constrained. Although hydrogen can have indirect greenhouse effects, its impact on global warming is lower than that of methane, especially in terms of short-term climate effects. Although many factors are still uncertain, it is likely that the overall carbon emissions of a high-purity source of natural hydrogen will be similar to or less than that of green hydrogen powered by renewable energy.

Cost to produce natural hydrogen

Value chains and life cycle analyses for natural hydrogen are still nascent – in part because of major remaining questions about the accessibility, distribution and scale of potential natural hydrogen use. The cost of natural hydrogen remains to be determined, as it has not been produced or sold in large quantities. Costs will depend upon several factors including scale of extraction, location and source purity. Natural hydrogen cost estimates are most typically directly compared against green hydrogen. While natural hydrogen would require energy and material inputs to extract, purify, transport and in some cases, store, the overall energy requirements for the entire life cycle may be significantly reduced in comparison to green hydrogen which is largely dependent on electricity sources used for processing. Another important factor in the cost is where the natural hydrogen is produced in relation to end-users. If other energy sources are expensive due to transport difficulties, or, in aid of decarbonisation, a local natural hydrogen source might be an attractive low carbon alternative. Overall natural hydrogen has the potential to diversify the global hydrogen supply.

Conclusions

1. Natural hydrogen is produced and accumulates underground by natural processes that can be accessed using established drilling methods and could be of economic potential if accumulated and stored in sufficient size reservoirs
2. There are many locations around the world that have the potential for natural hydrogen, but more research and exploration is needed to determine the extent and location of commercially viable fields (eg purity of hydrogen, volume, depth and accessibility)
3. Initial targets for economic exploitation of hydrogen may be most favourable in regional concentrated industrial hubs co-located on the same geologic settings where hydrogen accumulations have most often been found (eg iron-rich or iron-magnesium rich rocks that are already hubs for mining of gold, copper, nickel, diamonds or critical minerals)
4. The carbon emissions of natural hydrogen exploitation are likely to be similar to or lower than green hydrogen
5. The true cost of natural hydrogen remains to be proven, as it has yet to be produced and sold in quantity. Given a large enough reservoir of high purity hydrogen with easy access, published cost estimates suggest that natural hydrogen could be competitive with other colours of hydrogen
6. The UK currently lacks enough data and knowledge to conclude if it has significant natural hydrogen deposits. But as it has geologic settings with at least theoretical hydrogen producing potential, the UK can benefit and contribute to global momentum to understand and map hydrogen potential and prospects
7. Published data does not support the likely existence of an endless supply of natural hydrogen transiting from deep mantle sources and accumulating in accessible near surface reservoirs amenable for economic exploitation