����ֱ��

A new theoretical model developed by earth scientists at the University of Oxford, University of Toronto and Durham University may help alleviate a global supply shortage of helium – a naturally occurring gas critical for a wide range of medical, scientific and industrial applications, from cooling the magnets of MRI scanners to filling non-combustible balloons.

In , lead author and Oxford post-doctoral researcher Anran Cheng and colleagues explain for the first time how helium-rich gas fields form just beneath Earth’s surface and could help in locating untapped reservoirs around the world. Cheng completed this research as part of her doctoral work at Oxford, supervised by study co-authors Chris Ballentine at Oxford and ����ֱ�� University researcher Barbara Sherwood Lollar.

“Helium is in critically short supply worldwide, and current production methods are associated with significant carbon emissions that are contributing to climate change,” says Sherwood Lollar, in the department of Earth sciences in ����ֱ��’s Faculty of Arts & Science. “These results may enable the identification of alternative, carbon-free sources of helium that are accessible due to natural processes – and may lead us to new hydrogen sources, as well.”

Helium escapes from deep in Earth’s crust through bubbles of nitrogen gas diffusing from subsurface water. The process can take hundreds of millions of years, but when it happens these bubbles rise towards the surface due to helium’s buoyancy until they hit a rock type through which they can’t pass. According to the new model, the helium-rich gas bubbles then collect beneath the seal and can form a substantial gas field in the porous rock space beneath Earth’s surface.

By factoring in the presence of high concentrations of nitrogen gas – looking for nitrogen to find helium – the researchers for the first time used the model to determine the geological conditions necessary for the accumulation of nitrogen to become high enough to result in these helium-rich deposits. When the researchers applied the model to an example system – Williston Basin, a large sedimentary basin in North America – using expected nitrogen concentration values, the model predicted the observed nitrogen and helium proportions.

“This model provides a new perspective to help identify the environments that slow helium gases down enough to accumulate in commercial amounts,” says Cheng.

Helium is a US$6-billion market, with the gas being essential for the operation of MRI scanners, computer chips and fibre optic manufacture, as well as state-of-the-art nuclear and cryogenic applications. A current global shortage has pushed supplies nearly to a crisis point, with prices skyrocketing in recent years. The situation has been escalated by Russia’s invasion of Ukraine, as the new Amur gas-processing plant in Russia was to supply 35 per cent of the global helium demand.

In addition, almost all of today’s helium is a by-product of methane or carbon dioxide natural gas production. This carries a significant carbon footprint and hinders ambitions to achieve net-zero carbon emissions globally by 2050. In contrast, the naturally occurring nitrogen and helium-rich gases that were the focus of this study contain no methane or carbon dioxide, so tapping them does not release carbon emissions.

The model also suggests regions where large amounts of hydrogen gas may accumulate underground since the radioactivity that generates helium also splits water to form hydrogen.

“This new understanding of helium accumulation provides us with the critical start of a recipe to identify where significant amounts of geological hydrogen, as well as helium, might still be found,” says study co-author Jon Gluyas, professor at Durham University and executive director of the Durham Energy Institute.

With a global market of US$135 billion, hydrogen is used to create fertilizer and to produce many compounds essential for the food, petrochemical and pharmaceutical industries. Virtually all hydrogen gas is currently produced from coal and natural gas, and this alone accounts for 2.3 per cent of global carbon emissions. Hydrogen-rich underground deposits could provide an alternative carbon-free source.

“The amount of hydrogen generated by the continental crust over the last one billion years could power society’s energy needs for more than 100,000 years,” says Ballentine.

Sherwood Lollar adds, “Much of this hydrogen has escaped, been chemically reacted or used up by subsurface microbes – but we know from studying the gas in deep locations in the subsurface around the world that some of this hydrogen is indeed stored underground in significant quantities.”

The work was funded by the China Scholarship Council, the UKRI Oil and Gas DTP, the University of Oxford department of Earth sciences, the Natural Sciences and Engineering Research Council of Canada and CIFAR.

With files from the University of Oxford and Jon Gluyas.