An Evaluation on Phase Behaviors of Oil‐gas‐water System in The Displacement of Crude Oil with CO ₂

Abstract CO 2 dissolution into an aqueous phase and water evaporation into a gaseous phase takes place during CO 2 injection into an oil reservoir. This study aims to evaluate the phase behaviors of the oil‐gas‐water system in the displacement of crude oil by CO 2 . The composition of the JL oilfield in the northeast of China is taken as an example. The flash calculation of the oil‐gas‐water system was performed, based on the method presented by Li and Nghiem. The research results show that CO 2 dissolution in the aqueous phase declines as the NaCl concentration in formation water rises. CO 2 injection is beneficial for the evaporation of formation water. The NaCl concentration in formation water has little effect on water evaporation and dissolved‐gas escape. When the injection‐gas mole fraction of CO 2 is 0.5, CO 2 injection can reverse the phase behavior of the petroleum mixture and the oil‐gas system is converted to a pure gas‐condensate system. For CO 2 injection, water vapor has little effect on the miscibility of multiple contacts, but can reduce the miscibility of the first contact.