Effects of Permeability Heterogeneity on CO2 Sequestration In Brine Formation
Si-Yong Lee, Weon Shik Han, Chuan Lu, Brian McPherson, and Richard Esser. Energy & Geoscience Institute / Department of Civil and Environmental Engineering, University of Utah, 423 Wakara Way Suite 300, Salt Lake City, UT 84108
We present results of a study focused on the impacts of geologic heterogeneity on CO2 sequestration in deep saline formations. For systematic spatial variations in two-dimensional permeability (k) fields, we implemented 13 scenarios, including homogeneous, random, homogenous with a low-k inclusion, and anisotropically correlated random fields. Unlike previous studies solely based on a single realization, equally probable 10 realizations to each scenario except for the homogeneous cases were generated with sequential Gaussian simulation method and then served to the input for the numerical model of CO2 migration for a 200-year simulation period. To characterize the simulated CO2 plume behavior and associated trapping mechanisms, we divided and quantified the trapped CO2 as mobile-, residual-, and aqueous-trapped CO2. In addition, the first and second moments of CO2 plume distribution were examined to explore the both lateral and vertical CO2 displacement behavior according to the different geologic complexity. Simulation results from both homogeneous and uncorrelated random fields show distinct positive correlation between the effective vertical k and residual CO2 trapping. More interestingly, our results with the anisotropy in correlation length structure indicate that the degree of horizontal connectivity in log-normally distributed k fields tends to correlate with the amount of residual trapping only when the k anisotropy ratio of horizontal to vertical k was increased by one order of magnitude from the isotropic permeability. In contrast, no such strong relationship between the horizontal correlation length and residual trapping was found for isotropic permeability. This suggests that a brine reservoir with a longer lateral connectivity and greater k anisotropy ratio can better serve as a CO2 sequestration site in terms of residual trapping and buoyancy-driven migration.