Determination of Three-Phase Boundaries of Solvent(s)–CO₂–Heavy Oil Systems under Reservoir Conditions

Abstract

The liquid–liquid–vapor (L1L2V) phase boundaries of solvent(s)–CO2–heavy oil systems under reservoir conditions are experimentally and theoretically determined. Experimentally, the L1L2V phase boundaries of one CO2–heavy oil mixture, one C3H8–CO2–heavy oil mixture, and one n-C4H10–CO2–heavy oil mixture in the pressure–temperature (P–T) diagram are determined using a versatile pressure–volume–temperature (PVT) setup. The addition of an alkane solvent to the CO2–heavy oil system tends to expand the pressure and temperature span of the L1L2V phase boundary, while the L1L2V phase boundary of the solvent(s)–CO2–heavy oil system shows its tendency to move toward the high-temperature and low-pressure region of the P–T diagram. Theoretically, the previously developed binary interaction parameter (BIP) correlations for CO2–heavy oil binary, C3H8–heavy oil binary, and n-C4H10–heavy oil binary are incorporated into the Peng–Robinson equation of state (PR EOS) to determine the three-phase boundaries of the above-mentioned systems. The PR EOS with a modified α function and the BIP correlations is found to provide a generally good prediction of the experimentally measured L1L2V phase boundaries of the solvent(s)–CO2–heavy oil systems under reservoir conditions.