Multiphase boundaries and physical properties of solvents/heavy oil systems under reservoir conditions by use of isenthalpic flash algorithms

Abstract

In this paper, the newly developed techniques have been applied to determine multiphase boundaries and physical properties of solvent(s)/heavy oil mixtures at various pressures and temperatures in pressure–temperature (P-T), enthalpy-temperature (H-T), and pressure-enthalpy (P-H) phase diagrams, respectively. Theoretically, the Peng-Robinson equation of state (PR EOS) incorporated with a modified alpha function as well as the previously developed enthalpy calculation algorithm are used to predict the multiphase boundaries of the solvent(s)/heavy oil systems consisting of non-hydrocarbon solvents of CO2 and dimethyl ether (DME) as well as hydrocarbon solvents of C3H8 and n-C4H10. The PR EOS associated with the recently modified alpha function is found to be accurate in reproducing the experimentally measured VL1L2 (V represents the vapour phase, L1 denotes the high density hydrocarbon-rich liquid phase, and L2 refers to the low density CO2 liquid phase) three-phase boundary pressures with an overall absolute average relative deviation (AARD) of 2.01% and a maximum average relative deviation (MARD) of 4.34%, respectively. In addition, the VL1L2 three-phase boundaries are expanded and tended to move toward the region with higher temperatures and lower pressures in the P-T phase diagram with the addition of either C3H8 or n-C4H10 to CO2/heavy oil systems compared to those of only CO2 exists in heavy oil systems. Also, the new theoretical model developed in this study is able to reproduce the experimentally measured VL1 two-phase boundaries of alkane solvents/CO2/heavy oil mixtures as well as DME/heavy oil mixtures with an AARD of 4.52% and 2.88%, respectively. The enthalpy changes rapidly with variation of temperature in both H-T and P-H phase diagrams within the three-phase region.