Well-based, Geochemical Leakage Monitoring of an Aquifer Immediately Above a CO2 Storage Reservoir by Stable Carbon Isotopes at the Ketzin Pilot Site, Germany

We measured dissolved inorganic carbon (DIC) stable isotopes (813CDIC in ‰) of brine from an observation well within the first aquifer above the CO2 reservoir at the Ketzin pilot site, to test weather these can detect potential CO2 leakage. The monitoring revealed that DIC concentrations and 813CDIC values were masked by the used high alkaline drilling mud, even eight months after well development. However, subsequent changes in 813CDIC and DIC from of -27 ‰ and 165 mg L−1 to -23.5 ‰ and 116 mg L−1 reflect most likely a shift towards pristine values of the aquifer.