Determination of Three-Phase Boundaries of Solvent(s)-CO_2-Heavy Oil Systems under Reservoir Conditions

摘要

The liquid-liquid-vapor (L_1 L_2 V) phase boundaries of solvent(s)-CO_2-heavy oil systems under reservoir conditions are experimentally and theoretically determined. Experimentally, the L_1L_2V phase boundaries of one CO_2-heavy oil mixture, one C_3H_8-CO_2-heavy oil mixture, and one n-C_4H_(10)-CO_2-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 CO_2-heavy oil system tends to expand the pressure and temperature span of the L_1L_2V phase boundary, while the L_1L2V phase boundary of the solvent(s)-CO_2-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 CO_2-heavy oil binary, C_3H_8-heavy oil binary, and n-C_4H_(10)-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 a function and the BIP correlations is found to provide a generally good prediction of the experimentally measured L_1L_2V phase boundaries of the solvent(s)-CO_2-heavy oil systems under reservoir conditions.