Using the Kerr investigations at Weyburn to screen geochemical tracers for near-surface detection and attribution of leakage at CCS/EOR sites

Monitoring is cited as a mechanism by which operators can drive public acceptance in CO2 geosequestration and energy projects. In this synthesis study we inter-compared a broad suite of geochemical monitoring indicators, to identify which could contribute best to an affordable, yet effective, monitoring system. We examined two very comprehensive datasets, collected during a leak investigation, from a CO2 enhanced oil recovery (EOR) project in Weyburn, Canada, and applied an existing signal to noise ratio (SNR) approach to build a quantitative benchmark for each indicator. Despite the fact that a leak would be composed mostly of CO2, the analysis shows that a leak would be difficult to identify at this site based on CO2 or 13C-CO2, owing to the high variability of natural sources. Affordable alternatives such as N2, Ar, He, and CO2/O2 ratio would be less impacted by background variability. The most definitive indicators were 4He/20Ne (a proxy), and radiocarbon-CO2 (a direct indicator), though cost limits their everyday applicability. We conclude that a narrowed suite of indicators could achieve effectiveness at reduced cost, but that definitive indicators should be favoured in cases where leakage is suspected.