Determination of Multiphase Boundaries for Pressure–Temperature (P–T) and Enthalpy–Temperature (H–T) Phase Diagrams of C₃H₈/CO₂/Water/Heavy Oil Systems at High Pressures and Elevated Temperatures

Abstract

In this study, techniques have been developed to determine multiphase boundaries of C 3 H 8 /CO 2 /water/heavy oil systems in both the pressure−temperature (P−T) and enthalpy−temperature (H−T) phase diagrams. Experimentally, the upper three-phase boundary pressures (i.e., saturation pressures) between aqueous/liquid/vapor (ALV) and AL phases are measured for three C 3 H 8 /CO 2 /water/heavy oil mixtures. Moreover, the fluid samples in both L and V phases are collected to conduct compositional analysis by using a gas chromatography method. Theoretically, the previously developed waterassociated model, which considers only the presence of solvents with high solubility in water, together with the new alpha functions tailored for water and nonwater components is employed to predict the multiphase boundaries of the aforementioned systems. A newly developed enthalpy determination algorithm is applied to calculate the enthalpy of the Lloydminster heavy oil. The recently proposed water-associated model is capable of accurately predicting the upper three-phase boundary pressures of the three C 3 H 8 /CO 2 /water/heavy oil mixtures with a reasonable accuracy. As for the newly constructed H−T phase diagram, it is found that the three-phase ALV narrow-boiling region follows the trend of moving toward a higher temperature region with an increase of a specified pressure for a given feed. Finally, the water-associated model is proven to accurately reproduce the experimentally measured vapor and hydrocarbon-rich liquid phase compositions of the aforementioned systems.