Molecular dynamics simulation of supercritical CO 2 swelling and miscibility mechanisms in complex multi-component crude oil

Supercritical CO2 flooding has emerged as a core method for enhanced oil recovery in low-permeability reservoirs due to its efficiency and environmental benefits. While oil displacement mechanisms have been well-studied, microscale interactions remain unclear via traditional experimental methods. Most simulations focus on single-mechanism analyses, with limited exploration of how crude oil components and pressure conditions affect the process. Therefore, molecular simulation methods were employed to simulate injection pressure conditions at 15, 25, 40, and 55 MPa, using crude oil components from the Mahu-1 Wellblock in the Junggar Basin, Xinjiang. The swelling behavior was correlated with diffusion and swelling coefficients, and microscopic mechanisms were analyzed interaction energies. The miscibility was evaluated using density profiles. Results show that light crude oil components preferentially diffuse into CO2 at low pressures. Medium and heavy components, which contribute most to oil volume expansion, gradually disentangle and dissolve under the influence of dispersion forces as pressure increases. However, excessively high pressures hinder diffusion and reduce miscibility. These findings offer theoretical and practical insights for CO2 flooding in laboratory and field applications.