Phase Behaviour of Solvents/Heavy Oil Systems at High Pressures andElevated Temperatures

摘要

In this paper,techniques have been developed to determine multiphase boundaries of solvent(s)/heavy oilmixtures at high pressures and elevated temperatures in pressure-temperature(P-T),enthalpy-temperature(H-T),and pressure-enthalpy(P-H)phase diagrams,respectively.Theoretically,the Peng-Robinsonequation of state(PR EOS)incorporated with a new alpha function as well as the previously developedenthalpy calculation algorithm are used to predict the multiphase boundaries of the solvent(s)/heavy oilsystems by characterizing the heavy oil as a single pseudocomponent.The PR EOS associated with thenewly developed 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 tothe low density CO2 liquid phase)three-phase boundary pressures with an overall absolute average relativedeviation(AARD)of 2.01% and maximum average relative deviation(MARD)of 3.54%,respectively.Inaddition,the VL1L2 three-phase boundaries are expanded and tended to move toward the region with highertemperatures and lower pressures in the P-T phase diagram with the addition of either C3H8 or n-C4H_(10)toCO2/heavy oil systems compared to those of only CO2 exists in heavy oil systems.The enthalpy changesrapidly with variation of temperature in both H-T and P-H phase diagrams within the three-phase region.Either two-phase(VL1)or three-phase(VL1L2)isenthalpic flash calculations can be performed straightlyto determine phase fractions and compositions together with system temperature without conducting thestability analysis for a provided solvent(s)/heavy oil mixture at a constant enthalpy and pressure with theconstructed H-T phase diagram.