Helium and hydrogen gases are essential for medicine, high-tech industries, fertiliser for food security and a future net-zero society. Their production today is however chained to a large carbon footprint while, additionally, helium supply is in crisis. Together, these reasons mean that identifying alternative, carbon-free sources of natural helium has become critically important.
The challenge is that these lightest of gases easily escape from geological reservoirs given enough time. They are both escape artists. Houdini gases. Research led by Oxford Earth Sciences could help overturn the current supply crisis of helium without the large carbon footprint. This study proposes a new model to account for the existence of previously unexplained helium-rich reservoirs. The research defines a new concept in gas field formation and identifies the geological settings that these houdini gases can be found and tapped without emmitting carbon dioxide.
Helium has been produced to date as a rare minor gas separated during the production of methane or carbon dioxide natural gas fields. Helium is a $6 billion market 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 limited nodal supply chain compounded by a planned Russian supply of >30% of the global market has resulted in today’s helium supply to many users being turned off.
Hydrogen is used to create fertiliser and in the hydrogenation of compounds essential for the food, petrochemical and pharmaceutical industries. The global hydrogen market today is $135 billion. Greater than 99% of today’s hydrogen is produced by splitting off hydrogen from coal and natural gas (methane), and this alone accounts for 2.3% of global CO2 emissions. To supply the energy needs of a net-zero society, hydrogen demand could increase the annual hydrogen market to between $700-$1000 billion – but only if the hydrogen comes from non-CO2 emitting processes.
Helium is generated naturally over hundreds of millions of years in the continental crust by the decay of uranium and thorium found at very low levels in almost all rocks. The helium generated continually escapes because of its small atomic size and high diffusivity. Think of a helium filled balloon a few days after the party. When the helium reaches shallower levels of the crust, by itself it would be at concentrations so low that it would be dissolved in the water found in the rock’s pore spaces. Under these circumstances the helium continues to diffuse through the water in the interconnected pore space towards the Earth’s surface, where it either joins with hydrocarbon (methane) or carbon dioxide gases or reaches the atmosphere. Once in the air, because it is so light, helium escapes to space – another Houdini act.
This new research by scientists from the Universities of Oxford, Toronto and Durham however also considers nitrogen. Nitrogen is released from the deep crust along with helium. The authors identify the geological circumstances where the concentration of nitrogen can be high enough to create gas bubbles in the rock pore space. Such a process can take hundreds of millions of years, but when it happens the associated helium escapes from the water into the gas bubbles. The bubbles rise, because of buoyancy, towards the surface until they hit a rock type, or ‘seal’, that doesn’t allow the bubbles through (low permeability). The helium-rich gas bubbles collect beneath the seal and, the research shows, can form a substantial gas field when the overlying geological structures have the right shape (typically like an inverted bowl). These nitrogen and helium-rich gases contain no methane or carbon dioxide – and helium production is thus unchained from a carbon footprint. This new concept in gas field formation informs discovery of the locations, and gas compositions where such resources might be exploited.
Dr Anran Cheng, lead author of the study, says ‘The high diffusivity of helium and the long timescales it takes to accumulate enough gas means that we must view the entire geological system as a dynamic process. This perspective helps identify the environments that slow the gases down enough to accumulate commercial amounts, rather than expecting all the gas generated to be geologically trapped’.
The radioactivity that generates helium also splits water to form hydrogen. In addition, hydrogen is also generated in large quantities when water reacts with common iron-rich rocks. Prof Chris Ballentine, co-author, notes ‘The elephant in the room is hydrogen. The amount of hydrogen generated by the continental crust over the last 1 billion years (half the average age of continental crust) would power society’s energy needs for over 100,000 years.’ Prof Barbara Sherwood Lollar, co-author, tempers this by adding ‘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’. Prof Jon Gluyas, co-author, states that, ‘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.’
This work was funded by the China Scholarship Council, the UKRI Oil and Gas DTP, The University of Oxford Dept of Earth Sciences, NSERC and CIFAR (Canadian Institute for Advanced Research).
Featured image: Helium is a gas vital for MRI scanners and high tech industry – which is suffering from severe supply issues. Now research has identified a new concept in helium gas field formation that will help secure this rare gas for society. Here a tube of helium is seen glowing in the presence of a plasma ball. CREDIT: Oliver Warr – University of Ottawa; AEL AMS Laboratory
You can find the full paper at: https://www.nature.com/articles/s41586-022-05659-0