ABSTRACT
The main equations of the equilibrium reservoir flow of multicomponent systems were proposed approximately 30 years ago in publications by Bird, Steward, and Lightfood,1 Collins,2 Zheltov and Rozenberg,3 and Nikolaevskii.4,5 The equations used by these authors differ in general by the choice of fundamental variables. For example, Zheltov and Rozenberg used l – 2 mass fractions of components in the liquid phase as such independent variables,3 Collins used l – 1 overall mole fractions of the mixture components,2 and Nikolaevskii preferred the ratio of the mass fraction of the intermediate component in the liquid phase to the sum of mass fractions of the intermediate and heavy components in the liquid phase (for three-component systems).4 General thermodynamic analysis of the question about the number of independent variables in the multicomponent multiphase reservoir flow models, with and without taking into account the capillary forces, was carried out by Nikolaevskii based on the Gibbs approach.5
