Relative Importance of Heterogeneity, Anisotropy, and Permeability-Saturation-Pressure Constitutive Relationships During the Sequestration of CO2 in Deep Saline Aquifers

The feasibility of storing supercritical carbon dioxide (CO 2 ) in deep saline aquifers can be predicted via numerical simulation. The predicted behavior of injected CO 2 depends on factors such as heterogeneity of aquifer properties, anisotropy of horizontal and vertical permeability, and the permeability-saturation-pressure relationships ( k r – S – P c constitutive relations) that govern multi-phase flow. Although the importance of each of these factors has been investigated individually, their interactions are as of yet unclear. The objective of this paper is to quantify the relative importance of heterogeneity, anisotropy, and the k r – S – P c constitutive relations (specifically, van Genuchten’s m ) on the geologic storage of CO 2 in deep saline aquifers. We used TOUGHREACT to simulate the injection of CO 2 in an ensemble of realizations with different physical structure, anisotropy, and m . For each simulation, we assessed the pressure build-up observed during CO 2 injection, the maximum radial length traveled by the injected CO 2 plume, the percentage of CO 2 that is stored by solubility trapping, and the shape of the CO 2 plume. We found that heterogeneity and anisotropy have negligible influences on the CO2 behavior when m is low, but exert a strong impact when m is high. However, regarding the fraction of injected CO2 that is stored by solubility trapping, the extent of dissolution is mainly governed by m, while heterogeneity and anisotropy exert similar second-order impacts. The benefits of this work are to guide CO 2 emitters on the screening and selection of candidate repositories, and on the optimal allocation of resources for aquifer characterization. Particularly, characterizing the k r -S-P c relations may be as important as characterizing the permeability field.