Dissolution Trapping of Carbon Dioxide in Heterogeneous Aquifers

摘要

The geologic architecture in sedimentary reservoirs affects the behavior of density-driven flow and the dispersion of CO_2-rich brine. The spatial organization and connectivity of fades types play an important role. Low-permeability fades may suppress fingering and reduce vertical spreading, but may also increase transverse mixing. This is more pronounced when geologic structures create preferential flow pathways through connected fades types. We perform high-resolution simulations of three-dimensional (3D) heterogeneous formations whose connectivity cannot be represented in two-dimensional models consistent with percolation theory. This work focuses on the importance of 3D facies-based heterogeneity and connectivity on advection-diffusion transport of dissolved CO_2. Because the dissolution of CO_2 and the subsequent density increase of brine are the driving force for gravitational instabilities, we model the phase behavior with the accurate cubic-plus-association equation-of-state, which accounts for the self-association of polar water molecules and the cross-association between CO_2 and water. Our results eluddate how the spatial organization of fades affects the dynamics of CO_2 convective mixing. Scaling relations for the evolution of a global dispersion-width provide insights that can be universally applied. The results suggest that the long-term evolution and scaling of dispersion are surprisingly similar for homogeneous and (binary and multiscale) heterogeneous porous media.