An Evaluation of Phase Behaviors of the Oil-Gas-Water System in the Displacement of Crude Oil with CO_(2)

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.