For the past few years, companies and prospectors around the world have been hunting for underground reserves of natural hydrogen, spurred by estimates that Earth contains trillions of tonnes of the gas. If found, this geologic hydrogen could accelerate the transition away from fossil fuels. But despite a few tantalising hints that vast reserves exist, the search has largely come up short.
Until recently, most geologists didn’t see natural hydrogen as a potential source of energy. It had been measured seeping out of Earth’s crust in many places, such as in hydrothermal vents and mines, but not in huge amounts. The accidental discovery of a shallow reserve of natural hydrogen in Mali in 2012 demonstrated that bigger deposits could exist. But the consensus was that there wasn’t a sufficient amount produced underground to matter as an energy source; it was also thought unlikely that the reactive gas would regularly accumulate in large reservoirs before it seeped out or was gobbled up by microbes.
“What’s new now is that, suddenly, this bipedal life form, us, wants to compete with the microbes for the hydrogen,” says at the University of Toronto in Canada.
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The deposit in Mali remains the only substantial reserve of hydrogen that has been found. But at the US Geological Survey (USGS) says that doesn’t mean it’s time to write off geologic hydrogen just yet. “Finding reservoirs of fluid in the subsurface is not easy,” he says. And there is good reason to think large amounts exist.
In 2022, Ellis and at the USGS created a model to estimate how much natural hydrogen may exist, based on what was then understood about how the gas is generated underground. They found that the planet may hold anywhere from tens of billions to quadrillions of tonnes of hydrogen. This model indicated nothing about where the gas was generated, or whether it may have accumulated in underground pockets that would be feasible to tap into, but it implied that the possibility of using geologic hydrogen for energy had gone overlooked.
They have now published updated results from their model, largely with the same numbers as their original estimate, says Ellis. The most likely amount of hydrogen hidden underground is several trillion tonnes. If just 2 per cent of that could be tapped, the researchers calculate it would meet the entire global demand for the gas for centuries. That amount of hydrogen would contain more than double the energy contained within all proven reserves of fossil natural gas.
Despite these stunning estimates, however, the array of companies now searching for hydrogen everywhere from Nebraska to China have yet to find a viable reserve, particularly one big enough that would indicate geologic hydrogen might really be a new source of zero-carbon energy. Some companies – such as Gold Hydrogen in Australia and Française de l’Energie in France – have reported high concentrations of hydrogen in old wells originally drilled in search of oil and gas. And in Albania, researchers measured a record flow of hydrogen in a mine, which could indicate a deeper deposit.
But nobody has gone looking for a hydrogen reservoir and found one.
That is not hugely surprising given how long it usually takes to search for and exploit fossil fuel reservoirs, says at Stanford University in California. “I would be shocked if someone has found something.” It is also possible that companies have identified reserves, but haven’t shared the information publicly as they aim to secure rights to those resources. “Exploration is like a poker game,” says Awosiji. “A lot of people are holding their cards close to their chest.”
It’s also an expensive gamble. “The technology is there for drilling and extraction,” at the Advanced Research Projects Agency-Energy (ARPA-E) said at a meeting of the American Geophysical Union (AGU) in Washington DC. “The main challenge we have right now is estimating the size of [the] resource to convince the bankers.”
Still, enormous unknowns remain, not only about how much hydrogen may have accumulated in accessible reservoirs, but how much is produced within Earth in the first place. Ellis points out some of the more speculative parts of his 2022 estimates have been borne out by new research, such as evidence that hydrogen can be generated in some types of iron formations.
Other research suggests the amount of hydrogen might be more limited. For instance, at Miami University in Ohio has estimated the rate of hydrogen production from water reacting with different types of iron-rich rock. He found that while some rocks can generate substantial amounts of hydrogen, a lot of the iron gets used to form secondary minerals, limiting how much hydrogen can be produced from a given amount of iron. He presented his work on 12 December at the AGU meeting.
Some researchers are skipping the search for natural hydrogen entirely, focusing instead on stimulating production by injecting water, heat and chemicals into rock. Wicks, who directs a programme funding this research at ARPA-E, said early results are promising, though he didn’t offer specifics.
How long might it take before we know if geologic hydrogen will transform the energy system or be a bust? “That’s the big question everyone’s asking,” says Ellis. “I don’t know.”
Science Advances
