Engineered storage of anthropogenic CO2 within the subsurface requires the injection and storage of CO2 over a timescale of 1,000-10,000 years. To ensure the safety and security of the storage site it is essential that the injected CO2 can be monitored and traced during and after injection. Noble gases are conservative tracers within the subsurface, and combined with carbon stable isotopes, have proved to be extremely useful in determining both the origin of CO2 and how the CO2 is stored within natural CO2 reservoirs from around the world. The key aim of this fellowship was to identify and quantify how these natural tracers could be used to monitor future engineered CO2 storage sites.
The main output from my fellowship work is a means of testing for CO2 leaks from carbon storage sites. This test will allow the rapid detection of the source of CO2 should a leak from an engineered CO2 storage site be alleged, allowing the allegations to be quickly confirmed or denied. This test was developed by measuring the noble gases contained in CO2 rich waters collected from above the natural St. Johns Dome CO2 field. I determined that a component of the He fingerprint measured in gaseous CO2 sampled from the deep reservoir, could be traced along a fault plane to be present in the waters emerging at the surface above the CO2 field. This result showed for the first time that CO2 can be fingerprinted from source to surface using noble gases.