An improved component retrieval method for cubic equations of state with non-zero binary interaction coefficients for natural oil and gas

Abstract

Volumetric and equilibrium calculations for the natural gas and oil defined by a large number of components are not feasible in applications like compositional reservoir simulation. Therefore, the fluid mixture is grouped to reduce computational load and to make faster calculations. However, for several reasons, it is required to have the detailed fluid composition rather than the lumped one. In this work, an improved delumping method is presented to retrieve the phase composition of the detailed mixture based on the grouped mixture thermodynamic calculations. The method is based on previously proposed delumping techniques for non-cubic equation of state (Assareh et al. in Fluid Phase Equilib 339:40–51, 2013). To prepare lumped mixtures, a grouping technique, based on the components similarity, is used to classify the components with close critical properties and binary interaction coefficients in a pseudo-component (Assareh et al. in Int J Oil Gas Coal Technol 7(3):275–297, 2014). Afterward, a number of delumping parameters calculated from lumped system flash calculation are assigned to the components in a specific pseudo-component. The detailed mixture equilibrium ratios based on fugacity coefficient for a common cubic equation of state are calculated using these delumping coefficients. The accuracy of the method is verified on two petroleum reservoir fluids, a gas condensate and an oil reservoir fluid. The delumped equilibrium ratios were in good agreement with detailed ones with the absolute deviation of less than 2 %. The results confirm the applicability and accuracy of the presented method for detailed composition retrieval while simulating with pseudo-components.