Detection of simulated leaks from geologically stored CO2 with 13C monitoring

Abstract

Precise methods for the detection of geologically stored CO2 within and above soil surfaces are an important component of the development of carbon capture and storage (CCS) under terrestrial environments. Although CO2 leaks are not expected in well-chosen and operated storage sites, monitoring is required by legislation and any leakage needs to be quantified under the EU Emissions Trading Directive. The objective of the present research was to test if 13C stable isotope motoring of soil and canopy atmosphere CO2 increases our detection sensitivity for CCS-CO2 as compared with concentration monitoring only. A CO2 injection experiment was designed to create a horizontal CO2 gradient across 6m×3m plots, which were sown with oats in 2011 and 2012. Injected CO2 was methane derived and had an isotopic signature of −46.2‰. The CO2 concentrations were measured within the soil profile with passive samplers and at several heights within the crop canopies. The CO2 fluxes and their 13C signatures were also measured across the experimental plots. In situ monitoring and gas samples measurements were conducted with a cavity ring down spectrometer (CRDS). The plots displayed hot spots of injected-CO2 leakage clearly detectable by either concentration or isotopic signature measurements. In addition, the 13C signature measurements allow us to detect injected CO2 in plot regions where its presence could not be unequivocally ascertained based on concentration measurement alone.