Confinement Effects on Phase Behavior of the CO ₂ -Oil–Water System Using a Modified PR-HV Model

Accurately predicting the phase equilibria of the CO2-oil–water system is vital for simulating CO2-enhanced oil recovery and CO2 geological storage in shale oil reservoirs. However, conventional three-phase flash models have limited accuracy in predicting the phase behavior of the CO2-oil–water system because they neglect the nonideality of water and the strong interactions between CO2 and H2O. These limitations become more pronounced in shale nanopores, where the compression of intermolecular distances significantly intensifies interactions between CO2 and H2O. In this study, we develop a novel three-phase equilibria calculation model based on the Peng–Robinson–Huron–Vidal equation of state (PR-HV EoS). To enhance predictive accuracy under the confinement effects, the model modifies the PR EoS to characterize the confinement effects through a fluid–wall interaction coefficient and an adsorption effect coefficient, and employs the non-random two-liquid (NRTL) activity coefficient model to characterize the interactions between CO2 and H2O. Additionally, we propose two new critical property shift correlations by fitting 44 sets of experimental data. The example calculations show that the model proposed in this study has higher accuracy than the conventional three-phase flash algorithm. Overall, this model can accurately calculate the phase behavior of the CO2-oil–water system in nanopores, providing an effective phase equilibria model for carbon capture, utilization, and storage (CCUS) simulation in shale oil reservoirs.