Investigation of contact angle heterogeneity on CO2 saturation in brine-filled porous media using 3D pore network models

The sequestration of carbon in underground brine-filled reservoirs is a promising approach for reducing atmospheric greenhouse gas emissions. However, accurately estimating the amount of carbon dioxide (CO2) that can be captured remains a challenge. One difficulty lies in predicting the effects of capillary pressure variations on CO2 saturation arising from mineral contact angle heterogeneity inherent in geological formations. To determine the impact of these effects, the invasion of brine-filled porous media by supercritical CO2 was simulated using a three-dimensional regular-lattice pore network model. The effects of contact angle heterogeneity on CO2 saturation involving quartz and mica were modeled over a range of viscosity ratios (M) and capillary numbers (Ca) relevant to carbon sequestration. At Ca ∼ 10−4, CO2 saturation was 20% higher for heterogeneous contact angle distributions, compared to similar networks with homogeneous distributions. To quantify these results, we present power–law correlations for CO2 saturations in terms of M, whereby the introduction of contact angle heterogeneity affected both the coefficient and exponent of the best-fit power–law functions, at lower values of Ca. These results highlight the importance of micro-scale contact angle heterogeneity when sequestering CO2.