Impact of Relative Permeabilities on CO2 Geological Storage

Carbon Capture Utilization and Storage (CCUS) is considered an important technology that can abate and reduce the anthropogenic effects of CO2. The technology consists mainly in capturing the CO2 from high-intensity emissions sources and transporting it either to be utilized again as raw material or to be stored permanently in an adequate formation. The storing formations can be aquifers, oil and gas reservoirs, and coal mines. However, due to the abundant presence of aquifers, they are considered the main storage option for CO2. Once injected, the CO2 is trapped by a combination of several trapping mechanisms: the CO2 can be trapped structurally under the cap rock, residually due to the capillary forces acting on the plume, or it can be trapped in the aqueous or ionic phase due to its solubility in brine, which can eventually lead to the mineralization of the CO2. All of these mechanisms are affected by the plume size, shape, and migration trajectory. Thus the study of the effect of relative permeability and capillary pressure on the storage of CO2 is of high importance. For this purpose, a sensitivity analysis was performed by varying all the parameters that influence the relative permeability and capillary pressure curves. This study presents the results of the simulations performed on CMG’s GEM software of CO2 injection in an aquifer. The objective of our work was to better understand the effect of the relative permeability curves on the different trapping mechanisms. During the study, the following parameters were varied: swi, krCO2 (swi), C Land Coefficient, Pe, and Corey exponents. The simulations showed that the Land coefficient was the most impactful parameter on the CO2 storage mechanisms. It showed that a decrease in the LAND coefficient will lead to an increase in residual trapping and a decrease in both structural and solubility trapping. The variation of the kr endpoint had a limited impact on the final storage but showed an increase in residual trapping with a decrease in the endpoint relative permeability. As well, the increase of swi increased the residual and solubility trapping of CO2. Opting out the capillary pressure curves resulted in a decrease in all trapping mechanisms, while increasing the entry capillary pressure resulted in a decrease in residual trapping and an increase in solubility trapping. The shape of the relative permeability curve had some interesting effects on the storage mechanisms.