Modeling and calculation of thermodynamic properties and phase equilibria of oil and gas condensate fractions based on two generalized multiparameter equations of state

Abstract

Based on two generalized equations of state, previously developed by the authors, describing the properties of hydrocarbon chain and cyclic structures, a method for the predictive calculation of thermodynamic properties and phase equilibria of complex hydrocarbon mixtures (petroleum and gas-condensate fractions) has been developed. The method is applicable over a temperature range from the freezing point to 700 K and at pressures up to 100 MPa, including the liquid and gas phases as well as the supercritical region.The calculation of thermodynamic properties is made within the framework of the extended three-parameter corresponding states principle. The acentric factor was chosen as the third parameter of the corresponding states. The complex hydrocarbon mixture is treated as an individual substance, known as a “single-fluid model”. In this model, the mixture is a hypothetical individual hydrocarbon with an effective molar mass M and critical parameters, Tc, pc and ρc. This “substance” is characterized by the content of paraffin and cyclic structures in an effective molecule.For the calculation of phase equilibria, a method for modeling the composition of complex hydrocarbon mixtures using the concept of pseudo components has been developed. The method is based on the distillation curve and uses a minimum set of needed properties of mixtures, such as the average boiling temperature, relative density, and molar mass. Rules for generalization of the single-fluid model, used to calculate thermodynamic properties, to the linear model of mixtures, used for phase equlibria calculations, have been formulated.