The CO 2 -vadose project: Numerical modeling to perform a geochemical monitoring methodology and baseline performance assessment for various geochemical variables (gas flux, gas composition, stable isotopes and noble gases) in the carbonate vadose zone

The monitoring of CO2 storage sites is a paramount aspect for sites security and for the industrial deployment of the CCS technology. At the soil level, the monitoring of potential CO2 leakage will be requested, at least for high hazard areas (wells, faults). In this study, we compared the performance of a soil gas baseline survey with the disturbance in the gas composition and flux expected for a low amplitude diffuse leakage of CO2. A numerical study of a CO2 leakage was performed at the vadose scale by creating an underground CO2 source and observing its migration toward the atmosphere across a natural limestone formation. Only CO2 molecular diffusion in the gas phase and CO2 dissolution in the irreducible water were taken into account in this numerical model, following the description of a natural site on which field work was performed. A gas geochemistry baseline was performed in key locations and determined from the numerical predictions of the CO2 plume extension. In the light of the numerical experiment, we show how the different soil gas parameters measured are potentially useful for the detection of diffuse CO2 leaks at the soil level and we present the panel of different analyses and their respective addition to such studies. (C) 2013 Elsevier Ltd. All rights reserved.