Cemvita Factory, a biotech firm in Texas, had spritzed a carefully selected combination of bacteria and nutrients down the bore hole. Once inside the well, the microbes began breaking down the residual oil hydrocarbons in there—dregs that would be unprofitable to extract—to generate hydrogen and CO2. This field test in July, though small in scale, was a “huge success,” says chief business officer Charles Nelson. Nelson would not comment on what bacteria and nutrients the company is using, but he says his firm aims to produce hydrogen for $1 per kilogram, which would be competitive against other methods of obtaining the fuel. He estimates there are more than 1,000 depleted oil wells dotted around the United States that are suitable for the same kind of microbial treatment: “A lot of these reservoirs are abandoned, they’re in the custody of the state, they’re orphaned and waiting to be cleaned up.” Hydrogen, which releases zero carbon emissions when burned, has long been touted as a future fuel. Even though it’s the most abundant element in the universe, with copious amounts on the Earth’s surface in molecules such as water, some effort is required to obtain large quantities of pure hydrogen. There’s a long list of techniques currently vying for supremacy. People have taken to color-coding them, and there is now a veritable rainbow to choose from. There’s green hydrogen, where renewable energy is used to split water molecules into oxygen and hydrogen. Blue hydrogen, meanwhile, involves extracting hydrogen from natural gas. Cemvita Factory describes its product as “gold hydrogen”—“to pay homage to the past era of oil as the black gold and it now being used as a feedstock to make subsurface hydrogen,” says cofounder and CEO Moji Karimi. Nelson explains that the firm’s goal is to treat oil wells with bacteria to enable steady, long-term hydrogen production—perhaps lasting for decades. Existing, disused infrastructure above and around the well for taking off gasses could be brought back into service in order to collect the hydrogen, he adds. Capturing or otherwise neutralizing the CO2 must be done safely, says Stephen Wallace, who runs a microbiology lab at the University of Edinburgh. But he adds that Cemvita Factory’s idea of harnessing microbes for hydrogen production is “indicative of a lot of the really interesting work going on in biotechnology right now.” Wallace and his colleagues are themselves experimenting with bioreactors and have had some success in getting microbes to yield hydrogen from things like moldy bread or the lignin in paper industry waste. But while some microbes help produce hydrogen, others are the scourge of these projects, as they can eat up stored hydrogen or consume the gas in natural wells, says Jon Gluyas, a geologist at Durham University. “We’re trying to keep bacteria away from our hydrogen because they love feasting on it,” he explains. And he has another quibble. He argues that “gold hydrogen” is different from what Cemvita Factory is proposing. To Gluyas, that term refers specifically to hydrogen that has been produced naturally underground. He should know. “I named it,” he says. That Cemvita has given the same name to its hydrogen—which, the company makes clear, is “produced biologically, by microbes, and through a human-driven process”—is just a “coincidence,” Karimi claims. For more than a century, geologists have been pondering how much of the natural hydrogen to which Gluyas refers could be freely available in the ground beneath our feet. The German scientist Ernst Erdmann described in 1910 how he had detected an outflow of hydrogen at a salt mine and tracked it for four and a half years. But the possibility of widespread subterranean sources was still poorly understood, even into the 1980s, says Barbara Sherwood Lollar, a geologist at the University of Toronto. She recalls surveying sites for gasses back then and realizing that significant volumes of hydrogen were present in the ground. “Good lord, it was hydrogen, these rocks were full of hydrogen,” she remembers. Yes, the Earth hath bubbles. Since then, she and colleagues have mapped the locations of potential hydrogen sources—based on geology and known deposits—around the world. Different processes can give rise to natural hydrogen wells. One example is radiolysis, in which subatomic particles naturally emitted by radioactive rocks such as granite cause certain molecules to break apart, releasing hydrogen. In general, hydrogen is associated with crystalline rocks, rather than sedimentary ones. Some firms are already targeting hydrogen deposits, though—such as the company Gold Hydrogen in Australia. It estimates that there could be a total of 1.3 billion kilograms of hydrogen at depths of around 500 meters in the Ramsay Peninsula and Kangaroo Island in South Australia. There is also a large and well-known source of hydrogen in Mali. Both this and the Australian deposits are associated with “fairy circles”—where bare patches in the middle of vegetation indicate that hydrogen is coming out of the ground. Commercial extraction of hydrogen from any such locations, at scale, has yet to happen. Whether you call Cemvita Factory’s approach “gold hydrogen” or not, one advantage of it is that access to oil wells is reasonably straightforward—and they are often in well-serviced locations with nearby infrastructure for transporting gasses. Cemvita Factory is not the only firm to have considered this point. A completely different method of getting hydrogen out of old oil wells involves injecting oxygen into them to stimulate a flow of oil and chemical reactions that result in the production of hydrogen and other gasses. Canadian firm Proton Technologies has demonstrated this technique—which it refers to as “clear hydrogen.” Hydrogen production linked to depleted oil wells is interesting, but such projects are still at a relatively early stage, argues Richard Lowes, senior associate at the Regulatory Assistance Project, a clean energy NGO. “I’m initially skeptical, particularly when you can produce hydrogen quite easily with electricity—it’s just easier,” he says. And he questions whether such technologies could potentially shore up fossil fuel firms and fossil-fuel-related industries, in contrast to hydrogen production systems that rely on renewables. If new oil wells can eventually be transformed into green energy sources, they may appear more palatable. All of these ideas for obtaining hydrogen are currently jostling for attention—and investment. That, and the abundance of this crucial element in so many different places explains the rich color palette of hydrogens now emerging. From green to blue, gold, clear, and beyond, no one yet knows what will triumph. As Gluyas says: “We’ll probably have more colors than Crown Paints by the end of this process.”
