Carbon dioxide sequestration, otherwise known as carbon capture and storage or CCS, is one method of combating global warming which is caused by large amounts of CO2 in the atmosphere. Capturing and storing CO2 underground has the potential to eliminate decades of emissions. However, tracing the movements of CO2 underground may prove problematic. In a new paper published in the International Journal of Greenhouse Gas Control, researchers from the Scottish Universities Environmental Research Centre (SUERC) describe how they used the unique signature from traces of the noble gases (helium, neon and argon) to monitor the fate of carbon dioxide stored underground.
Carbon capture and storage (CCS) techniques aim to store carbon dioxide in depleted oil and gas fields or deep aquifers, preventing it from reaching the atmosphere. Also, injection of CO2 into depleted hydrocarbon fields has long been used for enhanced oil recovery (EOR).
The SUERC researchers collected gas samples from the largest non-power plant associated CO2-EOR field in operation in Cranfield, Mississippi, USA. The isotope composition of the naturally occurring noble gases (He, Ne and Ar) in the injected gas was measured in underground gases over three years of CO2 injection. These ratios track the movement of the injected CO2 through the reservoir and demonstrate that a significant proportion of the CO2 has been lost from the gas phase. The technique holds great potential for identifying and quantifying CO2 storage in future large-scale CO2 sequestration projects, as well as fingerprinting shale and coal bed-derived methane for environmental monitoring purposes.
Co-author Professor Finlay Stuart of SUERC (University of Glasgow) said: “We have shown for the first time that the naturally occurring helium, neon and argon in the injected gas is a unique ‘fingerprint’ that can be used to monitor the movement of the CO2, and determine how it is stored.
“Before CCS can become widely adopted as a method of CO2 mitigation we need to know how effectively the gas can be stored underground. The noble gases are chemically inert so they are not affected by interactions with rocks or water in the way that carbon dioxide is, so they can be used to identify the physical processes that have affected the gas. They provide a cheap way to fingerprint injected gases in future large-scale carbon storage projects, and have the potential to provide a unique way to track the presence of deep shale gas and coal bed-derived methane in shallow aquifers during and after extraction,” professor Stuart explained.
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