Pore-Scale Modeling of Coupled CO2 Flow and Dissolution in 3D Porous Media for Geological Carbon Storage

Dissolution trapping is one of the crucial trapping mechanisms for geological carbon storage in deep saline aquifers. The injected supercritical CO2 (scCO(2)) flow and dissolution processes are coupled and interact with each other. Therefore, we performed direct numerical simulations in three-dimensional micro-CT images of sandstones using the volume of fluid and continuous species transfer method. We investigated the coupled scCO(2) flow and dissolution processes at pore-scale under different rock structures, capillary numbers, and rock wettability conditions. The dynamic evolution of the scCO(2)/brine phase distribution and scCO(2) concentration distribution occurring during the injection period were presented and analyzed. Complicated coupling mechanisms between scCO(2)-brine two-phase flow and interphase mass transfer were also revealed. Our results showed that the scCO(2) dissolution was highly dependent on the local distribution of scCO(2) clusters. The rock with relatively high porosity and permeability would have more capacity for scCO(2) injection resulting in a faster and greater dissolution of scCO2 in brine. The effect of capillary number on the scCO(2) dissolution process was related to the range of capillary number. The effective upscaled (macro-scale) mass transfer coefficient (kA) during scCO(2) dissolution was evaluated, and the power-law relationship between kA and Peclet number was obtained. Rock wettability was found to be another factor controlling the scCO(2) dissolution process by affecting the scCO(2)-brine interfacial area. Our pore-scale study provides a deep understanding of the scCO(2) dissolution trapping mechanism, which is important to enhance the prediction of sequestration risk and improve sequestration efficiency. Storing carbon dioxide (CO2) underground reduces the concentration of CO2 in the atmosphere and helps to mitigate climate change. When CO2 is injected into underground formations, it can dissolve in the brine, helping to securely store it. In our study, we used numerical modeling on images of sandstone rocks to investigate how the CO2 flows in the rock and dissolves in the brine at the same time. In these simulations, we considered different rock structures, CO2 injection rates and rock "wetting" levels to study the effect on CO2 dissolution. Based on the simulation results, we concluded that the amount of dissolved CO2 depends on how it is distributed in the rock. Water-wetted rocks with more pores and higher permeability allow for more CO2 dissolution. Additionally, the amount of CO2 dissolution depends on the CO2 injection rate. Understanding these results helps to predict how effectively CO2 can be stored in underground formations. This knowledge is crucial for assessing the success and safety of carbon storage projects, ultimately contributing to reducing climate change impacts.