Predictions of three-phase regions in CO2-oil mixtures

Petroleum fluids can in the presence of CO2 present a complex phase behavior. Both two-phase (VLE and LLE) and three-phase regions (VLLE) might occur within certain ranges of pressure and temperature. important in EOR to be able to predict the phase behavior of these systems for both the design of CO2 flooding processes and reservoir simulation. No purely predictive method for the description of the three-phase region (VLLE) of these systems was previously reported in the literature. The correlation of experimental data has only been possible by means of a severe tuning of the oil properties or the equation of state employed. ictive model, using a cubic equation of state for description of the phase behavior of CO2-oil mixtures, is presented. A tuning procedure, based on the use of binary interaction parameters, was developed for systems where a fair description of the phase behavior is not achieved with the proposed model. It is shown that good predictions are usually obtained for temperatures below 314 K and that the tuning procedure can successfully describe the phase behavior in the remaining cases.