A method for calculating the phase equilibrium of hydrocarbon systems containing water

UDK: 622. © У.Р. Ильясов, А.А. Пашали, М.А. Литвиненко, 2022 НЕФТЕГАЗОВЫЙ
DOI: 10.24887/0028-2448-2022-5-90-93
Key words: three-phase equilibrium, phase state, phase composition, gas solubility, water content, Peng – Robinson equation of state, Huron – Vidal mixing rules, equilibrium constants
Authors: U.R. Ilyasov (RN-BashNIPIneft LLC, RF, Ufa), A.A. Pashali (Rosneft Oil Company, RF, Moscow), M.A. Litvinenko (Rosneft Oil Company, RF, Moscow)

Prediction of the phase state of multicomponent hydrocarbon systems containing water is an important aspect in modeling technological processes of field development. The presence of water in the composition of the extracted products can have a significant impact on the phase state, as well as on the numerical parameters of PVT properties. This can lead to a violation of the operating modes of the equipment, up to the occurrence of emergency situations. Modeling the phase state of multicomponent systems containing water or other polar substances requires the expansion of existing computational techniques and the development of new ones. The use of cubic equations of state is a generally accepted technique for modeling technological processes accompanying the development of deposits. One of the ways to expand the applicability of cubic equations of state for modeling systems containing polar molecules, such as water or alcohols, is the use of non-standard mixing rules, such as Kabadi – Danner, Huron – Vidal, etc., allowing for mutual dissolution of components in phases. The correct determination of the phase state, phase compositions, as well as PVT properties of hydrocarbon systems allows you to choose the optimal modes of operation of the equipment.

This paper presents the calculation method results of calculations of the phase equilibrium of multicomponent hydrocarbon systems containing water or other polar molecules. The results of a number of works are taken as a basis for calculating the equilibrium of binary systems "gas – water". An extension of the methodology has been carried out for the possibility of calculating the three-phase equilibrium "gas – oil – water" as well as special cases "gas – oil", "gas – water", and "oil – water". A system of equations for calculating phase equilibrium and determining phase fractions is obtained. Corrections for the initial values of the phase equilibrium constants are proposed. The results of calculations are compared with experimental data and the results of calculations in commercial software. Based on the results of the analysis, it is shown that this technique allows obtaining reliable results when modeling phase equilibrium, as well as for solving production problems. The implemented methodology is used in the corporate software complex RN-SIMTEP.


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