Natural hydrogen (H2) is sometimes called native hydrogen, geological hydrogen, or "white or gold" hydrogen. Hydrogen is a naturally occurring, odorless, colorless, and tasteless gas. (The assigned colors are just a construct to designate the source of the gas.) Emissions of natural hydrogen occur all over the world and have been know since Roman times. "The Eternal Flames" at Mount Chimaera in southwestern Turkey is a natural seepage of 10% hydrogen and 87% methane.
The government of South Australia reported that several early oil and gas exploration wells in that state tested high percentages of hydrogen gas:
- Robe-1: 25% H2 at 1241 m (4,072 ft) in 1915
- American Beach Oil-1: 64 to 80% H2 at 187 to 290 m (614 to 951 ft) in 1921
- Ramsay Oil Bore-1: 51 to 84% H2 at 241 to 508 m (790 to 1,667 ft) in 1931. (This accumulation was redrilled by Gold Hydrogen in 2023, with Ramsay-1.)
Worldwide interest in natural hydrogen exploration was spurred by the development of a shallow, natural hydrogen discovery in Mali, near the village of Bourakébougou, 60 km from Bamako, in Block 25. In 2011, the Bougou-1 discovery well was re-entered and tested. Sampling confirmed the gas as 98% hydrogen, with 1% nitrogen and 1% methane. This accumulation of natural hydrogen occurs within multiple host rocks reservoirs at depths varying from 30 to 1500 m (100 to 4,920 ft) and its performance over the first 5 years or so suggested a dynamic flow of natural hydrogen. This project became the world's first natural hydrogen-to-electricity project.
The presence of natural hydrogen has been confirmed in the Pyrenean foreland, the Jura, and Lorraine. As of December 2023, TBH2 Aquitaine was the first company to be granted a hydrogen exploration licence in France and there were an additional five licenses under investigation (Le Monde, 2023).
The Commonwealth Scientific and Industrial Research Organization (CSIRO) kicked off a research and development program in Australia in 2018 leading to revisions to the Energy and Resources Act and Regulations in South Australia in 2021. In the US, the first well targeting natural hydrogen was drilled in Nebraska by Natural Hydrogen Energy LLC in 2019.
The US Geological Survey (USGS) began investigating natural hydrogen resources in 2021. In 2024, active exploration campaigns are ongoing in Australia, Brazil, Colombia, the US, and various countries in Europe and Asia.
In a recent submission to the US Senate Committee on Energy and Natural Resources, Geoffery Ellis, the USGS lead hydrogen geologist, suggested that the probable distribution of in-place, global geologic hydrogen resources estimates was likely to have "an approximate mean value in the tens of millions of Mt." However, he also noted that the vast majority of the in-place hydrogen is likely to be in accumulations that are too deep, too far offshore, or too small to be economically recovered. "However," he added, "the remainder could constitute a significant resource."
Natural hydrogen is produced through natural, chemical, and/or biological processes, seemingly within an optimum temperature window for each process. They describe two conceptual models for the total natural hydrogen systems in the subsurface.
Model I – Shallow, Low-Temperature Hydrogen Sources
For either:
1) Iron-bearing rocks and radioactive ancient basement rocks
Here the generation of hydrogen is driven by serpentinization and/or radiolysis at relatively low temperatures (less than 100⁰C or 212⁰F), with water supplied by local hydraulic recharge or tidal pumping. The H2 generation process may be further enhanced in an existing fracture network or faults.
2) Geothermal activities, such as magmatic intrusions
Locally, geothermal activities may enhance the hydrogen generation by increasing temperature.
The generated hydrogen then migrates via both advection and diffusion.
For hydrogen generated by either:
3) Pyrolysis of organic matters or pre-existing hydrocarbons at high temperatures (more than 300⁰ C or 570⁰ F)
4) Degassing of the mantle via deep-seated, basement faults
The elevated temperatures are caused by deep burial and/or thermal events, which facilitate pyrolysis of organic matter or hydrocarbons. Such thermal conditions predominantly exist in extensional tectonic regimes, especially where thinning of the crust leads to high thermal gradients. These areas are also prone to magmatic thermal events or intrusions. Furthermore, these conditions are more likely to develop deep-seated faults, which serve as conduits for hydrogen originating from mantle degassing.
With either model, as the hydrogen tries to migrate to surface it may accumulate in structural (Figs. 1 and 2: 1, 2, 3) or stratigraphic (Figs. 1 and 2: 4) traps in the adjacent rocks or be absorbed by clay minerals (Figs. 1 and 2: 5). Due to the small size and extremely mobile properties of hydrogen molecules, almost any porous or naturally fractured rock is a potential storage reservoir. So, natural hydrogen accumulations may occur in sedimentary or nonsedimentary reservoir rocks or as absorbed gas in thick shales.
However, the reservoir-sealing mechanisms are challenging and will likely require dense igneous or metamorphic rocks, thick dense shales, or evaporites.
The identification and evaluation of natural hydrogen deposits is not easy. The petrophysical characteristics will vary enormously depending on the nature of the host rock, the connate water, natural hydrogen saturations, pressures, and temperatures, etc. Conventional reservoir quality rock containing free hydrogen gas can exhibit abnormally high neutron porosity, as observed in the shallow hydrogen-bearing carbonates (less than 100 m) at Bourakebougou Field in Mali. At depth, most of the natural hydrogen will be dissolved in the connate water, with which it can react to form hydronium ions (H3O+). (This occurs below 800 m [>2,625 ft] at Bourakebougou Field in Mali, for example).
Ross Crain states that petrophysical properties of natural hydrogen and hydronium are poorly understood. Potential hydrogen-bearing zones may be difficult to distinguish from water-bearing zones, except by mudlogging, but they will usually lead to a positive C1 reading. In new wells, gas chromatography can be used to confirm the H2 content in the drilling fluid returns.
For appraisal drilling, well testing is likely to be a key resource evaluation technique and should drive the well design, cost, and equipment selection. In some cases, it seems probable that the hydrogen will be coproduced with water, so that some form of artificial lift or a pump may be needed to initiate flow, as with coalbed methane or coal-seam gas wells.
The skid-mounted test separator and temporary flowlines will be like those used for any other well test, however, the equipment specifications may be different from those used in gas-well testing, if high concentrations hydrogen are anticipated, as in Mali.
Extended well testing to define the reservoir limits and/or the hydrogen recharge rates should ideally be carried out in a way that the energy is not wasted. In Mali, Hydroma used a portable generator to convert the produced fluids to electricity. Interestingly, Maiga et al. reported that after 11 years of production, there appeared to be a ±10% increase in reservoir pressure from 450 to 500 kPa (65 to 73 psi) in the pressure of the shallow zone that was on production.
Exploration and production for natural hydrogen requires many of the same skills and techniques as petroleum and mineral exploration. Hence, petroleum scientists and economists can contribute and transfer skills into natural hydrogen exploration.
Robert (Bob) Pearson, SPE, is an independent petroleum engineering advisor. He has extensive experience including field development planning and production engineering for onshore, shelf, and deepwater projects, as well as completions design for conventional and unconventional wells.
After working for 13 years for major operators, he has spent the past 40 years working as a consultant in Canada, Singapore, and Australia. He is currently dividing his time between Canada and the UK and provides advisory and peer-review services through Glynn Resources Ltd.
He joined the SPE Aberdeen Section in 1975 and was the 2019–2022 SPE Technical Director for Production & Facilities, and a former SPE Distinguished Lecturer. He currently serves as PetroWiki Interface on the board of the SPE Hydrogen Technical Section.
He holds a BSc with honors in mining engineering from the University of Newcastle-upon-Tyne in the UK and is a registered professional engineer with APEGA in Alberta, Canada.
Hongwen Zhao, SPE, is a staff researcher at Petronas Research Center in Malaysia. His current work focuses on the characterization of natural hydrogen systems and the development of H2 exploration strategies. With over 20 years of experience as a petroleum geologist and researcher, Zhao has worked with various oil and service companies in East Asia, North America, and the Middle East. His research interests include natural hydrogen exploration, clastic and carbonate diagenesis, rock typing, and complex reservoir characterization through the integration of geology, geochemistry, geophysics, and petrophysics. He is a member of SPE, AAPG, and EAGE.
He holds a PhD in carbonate sedimentology from the University of Alberta.
For Further Reading
Discovery of a Large Accumulation of Natural Hydrogen in Bourakebougou (Mali), by A. Prinzhofer, GEO4U; C. Cisse, Petroma; A. Diallo, Peroma.
Exploration for Natural Hydrogen, PetroWiki.
Natural Hydrogen Webinar, by Gabor C. Tari.
Natural Hydrogen, Government of South Australia Energy & Mining.
Natural Hydrogen: The Race To Discovery and Concept Demonstration by P. Ball and K. Czado, Geoscientist.
Natural Hydrogen Exploration in Australia by E. Frery, CSIRO Energy.
Molecular Hydrogen in Surface and Subsurface Natural Gases: Abundance, Origins, and Ideas for Deliberate Exploration by A. Milkov, Colorado School of Mines.
SPE 216710 The Hydrogen System in the Subsurface: Implications for Natural Hydrogen Exploration by H. Zhao, E. Jones, R. Singh, Petronas.
Hydrogen Emanations in Intracratonic Areas: New Guidelines for Early Exploration Basin Screening by I. Moretti, Laboratory of Complex Fluids; E. Brouilly, University of Rennes; K. Loiseau, Geosciences.
Hydrogen's Organic Genesis by J. Hanson, Haywards Health; H. Hanson, University of Brighton.
Characterization of the Spontaneously Recharging Natural Hydrogen Reservoirs of Bourakebougou in Mali by O. Maiga, E. Deville, J. Laval; IFP-School.