The application of noble gases and carbon stable isotopes in tracing the fate, migration and storage of CO2

The noble gases (He, Ne, Ar, Kr and Xe) are present in trace quantities in all natural and engineered CO2. They have proved to be extremely powerful tracers of both the CO2 source, and when combined with carbon stable isotopes, the subsurface processes that control the fate of CO2. Here we present a summary of the progress made over the past decade in using noble gases and stable carbon isotope tracing techniques in CO2 storage studies. We outline the initial lessons which were learnt from the study of natural CO2 reservoirs, then show the recent progress that has been made in tracing CO2 injected into a CO2-EOR field. We show the application of noble gases in determining natural CO2 leakage to the shallow groundwater and their use in successfully refuting the allegations of CO2 leakage made at the Weyburn CO2-EOR project. Our results illustrate that good progress has been made in using noble gases to determine both the short-term and long-term fate of CO2 in the subsurface and in the determination of the extent of groundwater interaction that the injected CO2 has undergone. However, there are still outstanding questions, particularly regarding the exact behaviour of the noble gases compared to CO2 and we show preliminary results from a laboratory study to investigate how noble gas transport through real rock compares to that of CO2.