Scientific and technical journal

«Proceedings of Gubkin University»

ISSN 2073-9028

Proceedings of Gubkin University

UDC: 622.276
DOI: 10.33285/2073-9028-2020-1(298)-47-61


Grigoriev Boris A.1,
Alexandrov Igor S.2,
Gerasimov Anatoly A.2,
Grigoriev Evgeny B.1

1 Gubkin Russian State University of Oil and Gas (National Research University), Moscow, Russian Federation
2 Kaliningrad State Technical University, Kaliningrad, Russian Federation

Keywords: density, heat capacity, saturation pressure, equation of state, reservoir fluid, oil, gas condensate


This article proposes methods for calculating the thermodynamic properties and phase equilibria of reservoir fluids based on both empirical multi-constant equations of state and theoretically based equations obtained in the framework of the statistical theory of associated fluid (SAFT). The article also proposes an alternative technique based on the author's generalized PC-SAFT equation of state. The article presents the results of comparative calculations of the thermodynamic properties of model hydrocarbon mixtures, as well as real reservoir systems based on the proposed methods. The most accurate calculation of thermodynamic properties in the single-phase region was shown by the multiconstant model. In particular, the accuracy of density calculation is 3-4 times higher than according to cubic equations of state. When testing this model regarding the calculation of phase equilibria, limitations were established that recommend its use for light gas condensates, in which the molar mass of the residue does not exceed 140 g/mol and the relative density of the residue does not exceed 0,730. For reservoir fluids that do not satisfy the condition described above, it is proposed to calculate phase equilibria using a model based on the author's PC-SAFT equation of state that can be used to calculate phase equilibria and near the freezing point of the mixture, where cubic and multi-constant equations can lead to nonphysical phase diagram.


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