What is natural hydrogen and how is it formed?

Natural hydrogen, also called white or gold hydrogen, is hydrogen gas produced by geological processes in the Earth's subsurface. It forms primarily through serpentinization of ultramafic rocks, radiolysis of water, and organic matter maturation, and can accumulate in natural reservoirs.

Where are the main occurrences of natural hydrogen found globally?

Significant natural hydrogen seeps and accumulations have been documented in countries including Mali, Brazil, Australia, Russia, the United States, and several European nations. Notable sites include the Bourakébougou field in Mali, where hydrogen is extracted for power generation, and seeps in the Mid-Atlantic Ridge and ophiolite belts.

What are the key geoscience challenges in exploring natural hydrogen?

Key challenges include understanding hydrogen migration and trapping mechanisms, identifying reliable geological indicators for accumulation, and developing detection methods for subsurface hydrogen reservoirs. The review emphasizes that hydrogen's small molecular size makes it prone to leakage, requiring specific cap rock and structural settings for preservation.

Is natural hydrogen a renewable resource?

Natural hydrogen is considered a potentially renewable resource because it is continuously generated by ongoing geological processes such as serpentinization and radiolysis. However, its renewability depends on the rate of generation relative to extraction, and current knowledge is insufficient to confirm sustainable yields for commercial use.

What is the estimated global potential of natural hydrogen?

Estimates of global natural hydrogen resources vary widely, with some studies suggesting vast quantities in the Earth's crust, but the review notes that recoverable reserves are poorly constrained. Current data indicate that while natural hydrogen is abundant in some geological settings, commercial-scale production remains limited to a few sites like the Bourakébougou field in Mali.

The Occurrence and Geoscience of Natural Hydrogen: A

Natural hydrogen, also called white or gold hydrogen, is molecular hydrogen (H₂) generated by natural geological processes within the Earth’s crust. It forms primarily through serpentinization of ultramafic rocks, radiolysis of water, and thermal decomposition of organic matter, and it accumulates in geological traps similar to those that hold natural gas.

How Natural Hydrogen Forms

The most widespread natural hydrogen production mechanism is serpentinization. When iron-rich mantle rocks, such as peridotite, are exposed to water at moderate temperatures (200–350°C), the iron in minerals like olivine oxidizes, and water is reduced to H₂. This reaction also produces serpentine minerals and magnetite. Serpentinization occurs in mid-ocean ridges, ophiolites (pieces of oceanic crust thrust onto continents), and Precambrian cratons.

A second important source is radiolysis. Radioactive elements in crustal rocks—uranium, thorium, and potassium-40—emit alpha particles that split water molecules, generating H₂. This process is slow but continuous, and it can produce significant volumes over geological time in deep, water-saturated basement rocks.

Thermal decomposition of organic matter (thermogenic H₂) also contributes. At high temperatures, kerogen and hydrocarbons break down, releasing H₂ alongside methane and other gases.

Geological Settings Where Natural Hydrogen Occurs

Natural hydrogen has been detected in several geological environments:

Precambrian cratons: Ancient, stable continental cores where deep fractures allow water to reach ultramafic rocks. Examples include the Canadian Shield and the Kaapvaal Craton in South Africa.
Ophiolite belts: Fragments of oceanic lithosphere emplaced onto continents. The Oman ophiolite and the Apennine ophiolites in Italy have shown H₂ seeps.
Rift zones: Areas of crustal extension where mantle rocks are close to the surface. The East African Rift System and the Rio Grande Rift have reported H₂ emissions.
Mid-ocean ridges: These ridges host extensive serpentinization and H₂ venting at hydrothermal fields.
Sedimentary basins: Some basins, such as the Paris Basin in France and the Kansas Basin in the United States, show H₂ in gas reservoirs, often associated with radiolysis or iron-rich shales.

Migration and Accumulation

Hydrogen molecules are very small and mobile. They can migrate through fractures, faults, and pore spaces in rocks. However, H₂ is also highly reactive and can be consumed by microbial activity or by reactions with minerals. For a significant accumulation to form, hydrogen must be generated faster than it is consumed or lost.

The same types of traps that hold natural gas—structural traps (anticlines, fault blocks), stratigraphic traps (pinch-outs, salt domes), and combination traps—can contain H₂. The key difference is that H₂ requires a very low-permeability seal, such as thick evaporite layers or tight shales, because of its small molecular size.

Reservoir rocks must have adequate porosity and permeability. Fractured basement rocks, karstified carbonates, and some sandstones have been identified as potential reservoirs.

Global Occurrence and Known Discoveries

Systematic exploration for natural hydrogen is still in its early stages, but several notable occurrences have been documented:

Bourakébougou, Mali: The only currently producing natural hydrogen well. It was discovered accidentally in 1987 during a water drilling project and has been producing H₂ for power generation since 2012. The reservoir is at about 100–180 meters depth, and the gas is 98% H₂.
Kansas and Nebraska, USA: Numerous wells drilled for oil and gas have encountered H₂ shows. In some cases, H₂ concentrations exceed 70% of the gas composition. The source is thought to be radiolysis in the Precambrian basement.
France (Lorraine Basin): Recent surveys have identified significant H₂ concentrations in deep boreholes.
Russia (Siberian Platform): H₂ seeps and accumulations have been reported in the Tunguska Basin and other areas, associated with Precambrian rocks.

Exploration Methods and Challenges

Exploring for natural hydrogen uses many of the same techniques as oil and gas exploration, with some modifications. Surface geochemical surveys measure H₂ concentrations in soil gas or shallow groundwater. Remote sensing can detect H₂ seeps through spectral signatures or by identifying characteristic mineral alterations.

Geophysical methods, including magnetic and electromagnetic surveys, help map ultramafic rocks and faults. Seismic surveys can identify structural traps. However, H₂’s low density and high diffusivity make seismic interpretation more challenging than for methane.

The main challenges are seal integrity, microbial consumption, and uncertain resource estimates.

Comparison with Other Hydrogen Types

Natural hydrogen differs from the more commonly discussed “green” (electrolytic) and “blue” (steam methane reforming with carbon capture) hydrogen. It is a primary energy source, not a secondary energy carrier. If extracted, it has a very low carbon footprint—only the emissions from drilling, pumping, and transportation.

Compared to green hydrogen, natural hydrogen does not require large amounts of renewable electricity or water. Compared to blue hydrogen, it avoids the need for natural gas feedstock and carbon capture infrastructure. However, the resource base is poorly constrained, and production rates depend on natural generation rates, which are slow on human timescales.

Key Takeaways

Natural hydrogen forms primarily through serpentinization of ultramafic rocks, radiolysis of water, and thermal decomposition of organic matter.
It occurs in Precambrian cratons, ophiolite belts, rift zones, and some sedimentary basins, often in structural or stratigraphic traps.
The only commercial production is in Mali, but numerous shows and seeps exist globally, especially in the US, France, and Russia.
Exploration uses adapted oil and gas methods, but challenges include seal integrity, microbial consumption, and uncertain resource estimates.
Natural hydrogen has a low carbon footprint but is a finite, naturally generated resource whose long-term sustainability depends on generation rates.

What Is the Occurrence and Geoscience of Natural Hydrogen: A Comprehensive Review