Process-based soil gas leakage assessment at the Kerr Farm: Comparison of results to leakage proxies at ZERT and Mt. Etna

Claims of CO2 leakage at the Kerr farm near the IEAGHG Weyburn-Midale CO2 Monitoring and Storage Project in Saskatchewan, Canada in 2011 presented an opportunity to test years of research in near-surface leakage detection in an operational setting. The claim was based on a study conducted by a private consultant that drew criticism from geologic CO2 storage experts. To assess the origin of the claimed leakage, a soil gas assessment was conducted at the site using a relatively new process-based soil gas approach (Romanak et al., 2012). In order to assess leakage without years of background data or complex statistical analyses, this simple approach uses three fixed soil gas ratios (augmented by isotopic and hydrocarbon data when needed). Using this approach at the Kerr site, the relative contributions of various processes creating soil gas geochemical signatures were determined including: (1) biologic respiration, (2) CH4 oxidation, (3) CO2 dissolution/reaction with carbonate, (4) mixing with atmosphere, and (5) CO2 leakage from the storage reservoir. For additional verification, the results of the Kerr assessment were compared to new data collected at the ZERT controlled release site in Bozeman, Montana and published data from a leakage proxy at the Mt. Etna volcano, Italy. The results from the Kerr site show no evidence for CO2 leakage from the storage reservoir and also verify that a process-based approach can be used to quickly and economically assess leakage above geologic carbon storage sites. In addition, data from the ZERT release suggest quantification of a leakage signal apart from natural processes may be most easily accomplished using a process-based approach.