Considered a mere geological curiosity just ten years ago, natural hydrogen is now the subject of a great deal of research and exploration. While the extent of the reserves is still being studied, evidence of its value in decarbonizing our economies is accumulating. What do we know today?
A totally decarbonized, rapidly renewable, inexpensive and 100% natural energy source is abundant just a few hundred meters beneath our feet: natural hydrogen.
Just ten years ago, the emanations of this gas from the Earth’s surface and from certain wells were considered anecdotal. Today, more and more players believe that it has the potential to be exploited and occupy an important place in our future energy mix.
Well-identified geological contexts
For a long time, it was thought that natural hydrogen, sometimes called “white hydrogen”, was generated essentially by two phenomena:
- Radiolysis, linked to the presence ofradioactive elements (uranium, thorium and potassium) in the rock, which emit radiation capable of transforming water moleculesH2Ointo hydrogenH2 and oxygen O2;
- Serpentinization is the oxidation, in the presence of water, of a mineral called olivine, found in oceanic crust. Coupled with a “water reduction” reaction, serpentinization can, like radiolysis, break water molecules and release hydrogen.
Serpentinization generally takes place at mid-ocean ridges, along which tectonic plates move apart due to the upwelling of mantle material, and where temperatures are very high. But it also takes place at a distance, in the ophiolitic nappes, when the oceanic crust finds itself in zones of compression due to plate tectonics. We now know that the temperature and pressure conditions prevailing in these areas, in the presence of water (reaching the heart of the rocks via faults), can generate hydrogen.
Map of ophiolitic nappes
Source: Isabelle Moretti, modified from Lévy et al (2023)
New sources revealed
But research is progressing, and we now know that natural hydrogen can also be generated in other geological contexts, such as cratons, an extremely ancient and stable part of the continental crust.
These cratons contain rocks rich in iron or, more generally, minerals, such as bandediron formations ( BIFs) or biotite-rich granites. In the presence of water, these iron atoms are directly oxidized, leading to water reduction. It is above this type of geological structure that the famous “witches’ circles” are often found, characterized by a lower density of vegetation. Observed in the United States, Russia and Brazil, these circles are often due to hydrogen emanations, some of them very significant.
Map of cratons likely to contain rocks rich in iron and radioactive elements
Stars indicate locations where hydrogen bound to this type of rock has been discovered, and black dots, locations of BIFs that often coincide with iron mines.
Source : Isabelle Moretti, modified from Lévy et al. (2023)
Other studies show that rapid serpentinization of olivine does not necessarily require high temperatures to generate hydrogen, thus considerably expanding the geological domains in which prospecting can be successful.
Finally, we now know that natural hydrogen can be formed in coals and other rocks rich in organic matter. When these rocks are buried, they generate hydrocarbons and then, at high temperatures, hydrogen which, under certain conditions, can remain in the free gas phase.
Supplying 25% of the world’s hydrogen consumption
If we consider only the hydrogen generated by new and old oceanic lithosphere and radiolysis – and therefore disregard production by BIFs and other iron-rich sedimentary or intrusive rocks and organic matter – researchers estimate that 23 million tonnes of natural hydrogen could be produced every year. That’s a quarter of the world’s hydrogen consumption. Australia alone could account for 6% of global needs.
How is hydrogen produced today?
Currently, 95% of hydrogen is produced from fossil fuels (coal gasification, hydrocarbon oxidation, steam methane reforming and natural gas), almost half of it from steam methane reforming (SMR). This is known as“grey” hydrogen . These processes are still the most cost-effective, but they also emitCO2 into the atmosphere. Today, there are two main alternatives for producing hydrogen with less impact on the climate:
- Blue” hydrogen (or “low-carbon hydrogen”) produced from fossil fuels (coal or natural gas) with capture and storage of theCO2 emitted (carbon capture, utilization and storage or CCUS);
- Hydrogen produced by electrolysis of water, either from nuclear energy (“yellow” or “low-carbon” hydrogen), or from wind or photovoltaic electricity (“green” or “renewable” hydrogen).
How is hydrogen retained in rock?
While the conditions under which hydrogen is generated in rock are now better understood, a number of questions remain as to how it can be exploited. Hydrogen is a very light, highly reactive gas, capable of diffusing through the rock and “leaking” into the atmosphere, where it becomes impossible to recover.
But the data is rather reassuring on this point. Observations made in Mali, Australia and France’s Pyrenees mountains show that there are impermeable “cover” rocks capable of slowing the ascent of this gas and even retaining it, thus enabling the formation of veritable hydrogen reservoirs. We know, for example, that salt or certain volcanic rocks called dolerites are perfectly impermeable to hydrogen. But other reservoir and rock blanket systems could also exist, and the installation of wells will enable us to discover them.
Flow or stock?
In addition, there is considerable evidence that hydrogen can be generated continuously, making it a “renewable” gas.
This is the case of the wells currently in operation at Bourakébougou in Mali, where production started over 10 years ago without any drop in pressure, proving that the reservoir(s) are constantly being recharged. This is also the case in Iceland, a region where the mid-oceanic wrinkle outcrops, and where the steam from geothermal power plants has been found to contain constantly-generated hydrogen.
As far as radiolysis is concerned, generation is slow, but the very long half-life of the rock’s radioactive elements suggests that they will continue to emit their radiation well beyond the human presence on Earth.
So it seems that, whatever the source, we’re dealing with a continuous flow rather than a limited stock.
Indispensable hydrogen
90% of the hydrogen produced worldwide today is used as a raw material in the chemical industry, in the manufacture of fertilizers (ammonia), solvents and fuels (methanol), and as a reagent in the refining of crude oil. But this percentage could well change, as producers of steel, cement, glass and metals consider using hydrogen to decarbonize their activities. Hydrogen could replace fossil fuels when electrification is not possible or too costly.
In the years to come, hydrogen could also be used as a fuel for road, rail, sea and air transport. Hydrogen is envisaged as a storage solution for intermittent energies (“green” hydrogen), when the production capacities of wind turbines and solar panels are surplus to requirements, or when kilowatts are cheap. Surplus electricity can be used to power hydrogen-producing electrolyzers, thereby enhancing the flexibility of the electricity mix.
Why is there so much interest in natural hydrogen?
Natural hydrogen is attracting so much interest because, at present, hydrogen synthesis poses a number of environmental, technical and economic problems that make it impossible to produce enough to meet demand.
Firstly, hydrogen produced from fossil resources has a problematic carbon footprint (see box How is hydrogen produced today?).
Secondly, further technical progress needs to be made in its synthesis by electrolysis using photovoltaic and wind power (green hydrogen) or nuclear energy.
Production costs are currently too high to make these low-carbon or renewable hydrogens competitive energy sources on the market. Steam Methane Reforming (SMR) or coal gasification may be unsatisfactory from an environmental point of view, but they are still highly effective in producing low-cost hydrogen.
Many advantages
Faced with this headache, natural hydrogen appears to be a particularly promising alternative.
First of all, it could be produced at low cost, as shown by the Hydroma project in Mali, where the price per kilo is a few tens of centimes, and the project in Spain, south of the Pyrenees, where it is advertised at 1 euro per kilo. Generally speaking, according to Isabelle Moretti, natural hydrogen should cost “ 30% less than one of today’s cheapest hydrogens ” (SMR), which is currently estimated at 2 dollars a kilo (1.89 euros), three times less than green hydrogen, the price of which continues to rise.
Secondly, it has two major advantages: it has a very low environmental impact, and it could well be very abundant. The various studies and explorations carried out over the last four years suggest that it is present in many parts of the world (see maps above), which could enable many countries to improve their energy independence and contribute to the decarbonization of their transport and industry.
Exploration accelerates in many countries
Natural hydrogen exploration is progressing most rapidly in South Australia (with companies such as Gold Hydrogen and 2H Ressources), but especially in the USA, in Nebraska, Arizona, New Mexico, Kansas and the Midwest (with companies such as Desert Mountain Energy, HyTerra and Koloma, backed by Bill Gates, Amazon and United Airlines). But many other countries have also entered the race, as the map below shows.
Source: Wood McKenzie, July 2024
France leads the way
” In France, natural hydrogen has been on the statute books since 2022, and the first permits have been issued for both hydrogen and helium ,” explains Isabelle Moretti.
Emmanuel Macron, for whom ” we can’t let this resource lie dormant “, announced in December 2023 “ massive funding to explore the potential of white hydrogen “. Several emanations of this gas have indeed been detected in France, in the Pyrenees, Cotentin, Drôme and Lorraine regions.
On December 3, 2023, startup TBH2 Aquitaine became the first company to obtain an exclusive research permit (PER) for natural hydrogen in the Atlantic Pyrenees. Called Sauve Terre H2, this is “France’s first 100% natural hydrogen exploration project “, explains Isabelle Moretti. Over a period of 5 years, it should enable us to assess the quantities of hydrogen hidden in the subsoil of the Béarn region. Storengy and start-up 45-8 Energy have also applied for a PER project nearby, again in the Atlantic Pyrenees. And Sudmine has filed two, one in theAin and the other in the Puy-de-Dôme (lithium and natural hydrogen).
In Lorraine, there are also some good clues. Researchers at the GeoRessources laboratory in Nancy have identified a high percentage of dissolved H2 in an aquifer at the Folschviller well. In May 2023, GeoRessources and Française de l’Énergie (FDE) applied for a 5-year PER ( Permis des Trois-Évêchés ) in the Lorraine mining basin.
A game changer?
Although it’s still in its infancy and many uncertainties remain, natural hydrogen, as an affordable primary energy resource, could well revolutionize the decarbonized hydrogen sector.
Is an energy revolution on the horizon? The next ten years should tell us…
Source:
- Isabelle Moretti, Hydrogène naturel : son exploration-production a commencé, quelles sont les perspectives, La revue de l’Énergie, n°667, July-August 2023.
- White hydrogen, the potential of an energy revolution for France?, Gaëlle Ménage, Forbes, May 21, 2024.
- Hydrogen production, Connaissance des énergies, June 2024.
- L’essentiel sur l’hydrogène, CEA, September 2024.