New research from the University of Edinburgh shows that the movement of carbon dioxide underground can be tracked using naturally occurring noble gases.
Carbon capture, utilisation and storage (CCUS) is a method by which waste CO2 emissions from heavy industry is captured and injected into geological structures underground. Now, a team has demonstrated that naturally occurring noble gases could be used to provide a reliable monitoring technique.
It is vital for storage operators to monitor the stored CO2 and to ensure that it is secure, so as to avoid the negative environmental consequences that would occur following a leak. To do so, operators must be able to determine the carbon dioxide’s source and follow its movement.
How can noble gases track the movement of CO2?
The team’s discovery about the role of naturally occurring noble gases stems from previous research which demonstrated that chemical tracers can provide a type of ‘fingerprint’ for CO2.
This research showed how stored carbon dioxide can easily be distinguished from natural sources, but because the movement of the chemical tracers underground was not well understood, their effectiveness as a means of tracing the movement of migrating CO2 could not be shown.
In research published in the journal Chemical Geology, the team from the University of Edinburgh tested how quickly a number of chemical tracers could travel through a block of sandstone, testing naturally occurring noble gases against the industry standard tracer, sulphur hexafluoride.
It concluded that all of the tracers tested moved more quickly than carbon dioxide, and that, if these tracers were to be injected into CO2 before storage, movement of the gas could be quickly detected by CCUS storage operators.
What did the team say about the discovery?
Dr Stuart Gilfillan, who co-ordinated the study at the University of Edinburgh’s School of GeoSciences, said that the team’s discovery could be a vital step towards better security in CCUS: “This new knowledge about the behaviour of CO2 and tracers in the subsurface will help in the development of monitoring techniques to ensure secure carbon storage”.
The naturally occurring noble gases krypton and xenon were shown to be as effective as sulphur hexafluoride as a tracer, but do not carry the same negative environmental impact.
Gilfillan explained: “We found that the time taken for krypton and xenon to flow through the rock sample was almost identical to that of the standard industry tracer, sulphur hexafluoride. As sulphur hexafluoride is a potent greenhouse gas, our results show that climate-friendly krypton and xenon can be used instead in future tracing applications.”
