Utility of natural and artificial geochemical tracers for leakage monitoring and quantification during an offshore controlled CO2 release experiment

To inform cost-effective monitoring of offshore geological storage carbon dioxide (CO2), a unique field experiment, designed to simulate leakage CO2 from sub-seafloor reservoir, was carried out in the central North Sea. A total 675 kg were released into shallow sediments (?3 m below seafloor) for 11 days at flow rates between 6 and 143 d-1. set natural, inherent tracers (13C, 18O) injected added, non-toxic tracer gases (octafluoropropane, sulfur hexafluoride, krypton, methane) used test their applicability attribution quantification marine environment. All except 18O capable attributing source. Tracer analyses indicate that dissolution sediment pore waters ranged 35 % lowest injection rate 41% highest rate. Direct measurements gas water column suggest 22 48 exited seafloor at, respectively, The remainder accumulated pockets sediment. methodologies can be rapidly confirm source leaking once seabed samples are retrieved.