Above, still from a great interactive visual at Chem and Engineering News, click the link here to access.
Stories about reservoirs of natural hydrogen are true, and the resource may be enormous – no one’s ever bothered to characterize it before. It’s not a slam dunk, some of it contains levels of methane that complicate recovery. But if the Hunt for “Gold” hydrogen pans out, the rewards are immense.
Chem and Engineering News:
The hydrogen found underground gets there by a handful of chemical mechanisms. In the most important one, rock rich in iron(II) and magnesium comes into contact with water at elevated temperature and pressure. If conditions are right, electrons transfer from the iron to the water, resulting in molecular hydrogen, iron(III) oxides, and silica compounds.
Geochemists call the process serpentinization because it produces serpentine minerals such as antigorite, lizardite, and chrysotile, which often have a scaly appearance. The best minerals for serpentinization are mafic and ultramafic rocks, which feature magnesium and chromium alongside the iron and silicon. Manganese, cobalt, and nickel are often present in these rocks as well.
Radioactive decay of uranium, thorium, or other elements can also split water and form hydrogen, albeit much more slowly than serpentinization. The resulting hydrogen accumulates in porous rock such as sandstone that lies underneath impermeable layers made of rock such as shale or salt. Researchers also think Earth’s core and mantle shed primordial hydrogen into the planet’s outer layers through tectonic faults (Annu. Rev. Earth Planet. Sci. 2001, DOI: 10.1146/annurev.earth.29.1.365)
The chemistry and geology get complicated quickly, which is why the nascent industry is excited about a new set of studies from the US Geological Survey (USGS). The first looks at the mechanisms by which hydrogen is created, consumed, and released deep underground to estimate the quantity that is made each year and how much might be trapped in reservoirs like the one in Bourakebougou (Sci. Adv. 2024, DOI: 10.1126 /sciadv.ado0955).
The researchers, led by USGS staffers Sarah E. Gelman and Geoffrey S. Ellis, calculate that about 5.6 trillion metric tons (t) are trapped in geological formations around the world and that another 15 million–31 million t emerge every year. Ellis testified about the results before the US Congress in February 2024.
The researchers emphasize that most of the hydrogen isn’t economically accessible, but because the volumes are so huge, harvesting even a small percentage could make a big impact on climate change, they say. “We calculate the energy content of this estimated recoverable amount of hydrogen to be roughly twice the amount of energy in all the proven natural gas reserves on Earth,” they write in the paper.
Today, most commercially-available hydrogen is produced from natural gas. This “grey” hydrogen is relatively energy-intensive and releases about 10 tons of carbon dioxide to the atmosphere for every ton of hydrogen gas generated. Until recently, additional hydrogen was projected to come from a combination of hydrogen derived from natural gas, coal, or biomass coupled with carbon capture and sequestration (“blue” hydrogen), and hydrogen generated by electrolysis of water using renewable sources of electricity (“green” hydrogen).Today, my testimony will focus on a previously overlooked source of hydrogen: naturally occurring geologic hydrogen accumulations in the Earth’s subsurface (“white” or “gold” hydrogen).
The USGS has recently developed a model of global hydrogen resource potential. The model is based on known properties of hydrogen and well-understood accumulations of other geologic resources, including petroleum, geothermal energy, and noble gases such as helium. These factors provide some constraints on the possible magnitude of the global geologic hydrogen.
The USGS has recently developed a model of global hydrogen resource potential.
The model is based on known properties of hydrogen and well-understood accumulations of other geologic resources, including petroleum, geothermal energy, and noble gases such as helium. These factors provide some constraints on the possible magnitude of the global geologic hydrogen resource in the Earth’s crust.
Estimated in-place2 global geologic hydrogen resources range from
thousands to billions of metric tons (Mt), with an approximate mean value in the tens of millions of Mt. The model does not predict the spatial distribution of hydrogen in the subsurface.
Based on historical data on other geologic energy resources, the vast majority of the in-place hydrogen resource is likely to be in accumulations that are too deep, too far offshore, or too small to be economically recovered. However, the remainder could constitute a significant resource.