Modeling the Drying Process of CO2-Water in Porous Media With a Novel Volume-of-Fluid Lattice Boltzmann Model

Abstract

Lattice Boltzmann (LB) modeling has been extensively applied to porous media processes, including evaporation. Former pore-scale LB models for evaporation rely on oversimplified assumptions, such as matched viscosities. However, in subsurface CO2–brine systems, the viscosity ratio can exceed 100 under relevant temperature–pressure conditions. This study introduces a novel LB model based on the Volume-of-Fluid (VoF) method, capable of simulating two-phase flow in porous media with high-contrast viscosities and densities. The proposed VoF-LB model was further extended to model coupled evaporation and two-phase flow for water–CO2 in porous media. The simulation results were validated against analytical benchmarks and a pore-scale micromodel experiment. The model was employed to explore how pore size distribution variability influences the drying front and the redistribution of water due to capillary suction, with implications for geological CO2 storage in saline aquifers. This study presents two key advancements: (a) it demonstrates that the developed VoF-LB model accurately captures sharp phase interfaces and effectively handles extreme viscosity and density contrasts relevant to CO2–water systems; (b) the validated VoF-LB model is applied to simulate drying in both 2D and 3D porous media, introducing a dimensionless parameter to quantify evaporation-driven mass transfer relative to capillary flow. The results reveal that pore-size heterogeneity and capillary-pressure gradients play a crucial role in shaping the drying interface and governing water redistribution. In 3D simulations, greater water-phase connectivity amplifies these effects compared to 2D, highlighting the significance of corner flow and extensive liquid connectivity—phenomena not fully captured in 2D.