Phase behavior and mass transfer mechanisms of CO2 multicomponent gas and crude oil system

The large-scale deployment of carbon capture, utilization and storage (CCUS) technologies and the growing demand for low-cost gas sources provide new opportunities for the development of CO 2 multicomponent gas flooding. However, the interphase mass transfer mechanisms between CO 2 multicomponent gas and crude oil system remains unclear. In this work, non-equilibrium and equilibrium phase experiments, equation-of-state calculations, molecular dynamics simulations, and reservoir-scale numerical simulations were combined to investigate the phase behavior and mass transfer mechanisms of CO 2 multicomponent gas and crude oil system. The results show that non-equilibrium systems exhibit spatially heterogeneous local mass transfer. CO 2 demonstrates the strongest dynamic mass transfer capacity, while under the same conditions, the dynamic mass transfer effect of N 2 is extremely weak. The extraction effect of CO 2 multicomponent gas on hydrocarbon components in crude oil exhibits a nonlinear “critical response”. When the CO 2 mole fraction reaches a critical extraction threshold of approximately 70%, the overall extraction capacity of the system increases significantly, and heavy hydrocarbon components are more sensitive to changes in CO 2 concentration. As the crude oil becomes lighter, oil displacement efficiency exhibits weak dependence on the extraction of heavy components by the multicomponent gas. This study provides a theoretical basis for optimizing multicomponent gas composition and selecting low-cost gas sources, and offers a valuable guidance for the field application of CO 2 multicomponent gas flooding.