Optimizing CO2 Trapping in Geological Carbon Sequestration by Reducing Nonwetting Phase Connectivity

Abstract:

Decreasing the carbon in the atmosphere has become an increasingly vital step in mitigating climate change. The most recent IPCC report states that the goal of keeping global temperature rises to 1.5°C above pre-industrial temperatures will likely fail if negative emission strategies such as carbon capture and storage are not utilized. Geological carbon sequestration can take place on a relatively short geological timescale through the capillary trapping mechanism, which securely traps the CO₂ in the subsurface. Capillary trapping was studied by conducting experiments using proxy nonwetting and wetting fluids, representing the supercritical CO₂ and brine in the subsurface, respectively. It has been shown that increased trapping can stem from reduced topological connectivity of the CO₂ after injection. Therefore, the proxy nonwetting and wetting fluids of Soltrol 220 and water, respectively, were used to model a reduction in connectivity of the injected fluid. Variable drainage and imbibition flowrates were utilized to determine the combination of flowrates that results in the lowest post-secondary imbibition nonwetting fluid (CO₂ proxy) interconnectivity. The experiments were conducted using a sintered glass bead column, which were scanned four times for each flowrate combination using x-ray computed microtomography (microCT). The column was scanned prior to fluid injection, following the primary imbibition stage, and at the end of the drainage and secondary imbibition stages. These scans provide insight regarding the pore-space and an assessment of the relative effectiveness of trapping for the various employed flowrates. Lower injection flowrates for both the nonwetting and wetting fluids are anticipated to lead to a decrease in overall connectivity of the nonwetting phase, due to the snap-off phenomenon. Therefore, lower injection flowrates are expected to result in higher residual saturation of the nonwetting phase, i.e., trapped CO₂. This research could have implications for geological carbon sequestration methods and their ability to more efficiently sequester CO₂, thereby further reducing the effects of climate change.