Improved single-field VOF method for interfacial mass transfer modeling: Application to CO₂-EOR and carbon sequestration in hydrocarbon reservoirs

In enhanced oil recovery and carbon sequestration processes, interfacial mass transfer involved in CO₂ displacement plays a critical role. However, accurately characterizing and simulating such interfacial phenomena remains challenging due to the complex coupling between two-phase flow dynamics and phase behavior caused by gas component transport. This study introduces an improved single-field pore scale approach within the VOF-CST framework to model species dissolution and diffusion in CO₂-oil two-phase flow. The presented method couples interfacial mass transfer through a source term in the governing equations and introduces an additional symmetric term to control the effective interface movement. The approach is validated by comparing the results to the analytical solution for pure gas dissolution in an immiscible gas-solvent system in a one-dimensional tube. The first application case explores oil swelling during static diffusion in a micro PVT tube, demonstrating great agreement with the experimental results. Secondly, the formation and remobilization of dead-end oil clusters are considered, providing insights into CO₂-EOR mechanisms during cyclic CO₂ injection. Finally, we simulate CO₂ injection in a complex 2D porous model. The fluid distribution evolution and effective mass exchange coefficients were examined and calculated. Results show that oil mobilization is primarily driven by drainage mechanisms, with significant flow diversion effect observed after breakthrough. This work presents a robust computational framework for investigating interface-dominated multiphase transport phenomena, with direct applications to enhanced oil recovery and geological carbon storage.