Integration results of soil CO2 flux and subsurface gases in the Ressacada Pilot site, Southern Brazil

Abstract The first CO 2 monitoring field lab at the Ressacada Farm, in the Southern region of Brazil, started in 2011 and until 2015 offered an excellent opportunity to run controlled CO 2 releases experiments in soil and shallow subsurface through vertical injection wells. This paper focus on the presentation and comparison of the results obtained at the last campaign realized at this site in August 2015. The results integrate a time-lapse monitoring experiment of CO 2 migration in both saturated and unsaturated sand-rich sediments and soil, using soil CO 2 flux measurements and subsurface gas analyses through CO 2 concentrations (ppm) and carbon isotope ratios (δ 13 C of CO 2 ). The CO 2 flux results in the studied area showed an increase in the flux values according to the increasing of injection rate and along the campaign are directed to the southwest portion of the area. However, even by injecting large amounts of CO 2 , fluxes are greatly reduced when it rains. The gas analysis also showed an increase in CO 2 concentrations according to the increasing of the injection rate mainly in the superficial levels of the monitoring wells (0.5m and 2m depth). The δ 13 C of CO 2 found on the 3 rd injection day showed the presence of CO 2 injected and demonstrate that the sampling methodology with vacutainer vial was effective, since there is no atmospheric contamination. The correlation of isotopic analysis were consistent with the results of concentrations and CO 2 fluxes and thus, it is clear that the CO 2 breakthrough occurred from the 3 rd day of injection, while were obtained the largest CO 2 fluxes, the higher gas concentrations in the subsurface, as well as the industrial origin of δ 13 C of CO 2 .