Pore-scale numerical simulation of supercritical CO2-brine two-phase flow based on VOF method

CO₂ capture and storage technology is favorable for the reduction of CO₂ emissions. In recent years, a great number of research achievements have been obtained on CO₂ geological storage from nano scale to oil/gas reservoir scale, but most studies only focus on the flow behaviors in single-dimension porous media. Besides, the physical experiment method is influenced by many uncertain factors and consumes a lot of time and cost. In order to deeply understand the flow behaviors in the process of CO₂ geological storage in microscopic view and increase the volume of CO₂ geological storage, this paper established 2D and 3D models by using VOF (Volume of Fluid) method which can track the dynamic change of two-phase interface, to numerically simulate supercritical CO₂-brine two-phase flow. Then, the distribution characteristics of CO₂ clusters and the variation laws of CO₂ saturation under different wettability, capillary number and viscosity ratio conditions were compared, and the intrinsic mechanisms of CO₂ storage at pore scale were revealed. And the following research results were obtained. First, with the increase of rock wettability to CO₂, the sweep range of CO₂ enlarged, and the disconnection frequency of CO₂ clusters deceased, and thus the volume of CO₂ storage increased. Second, with the increase of capillary number, the displacement mode transformed from capillary fingering to stable displacement, and thus the volume of CO₂ storage increased. Third, as the viscosity of injected supercritical CO₂ gradually approached that of brine, the flow resistance between two-phase fluids decreased, promoting the "lubricating effect". As a result, the flow capacity of CO₂ phase was improved, and thus the volume of CO₂ storage was increased. Fourth, the influence degrees of wettability, capillary number and viscosity ratio on CO₂ saturation were different in multi-dimensional porous media models. In conclusion, the CO₂-brine two-phase flow simulation based on VOF method revealed the flow mechanisms in the process of CO₂ geological storage at pore scale, which is of guiding significance to the development of CCUS technology and provides theoretical guidance and technical support for the study of CO₂ geological storage in a larger scale.