Simulation of Compositional Processes: The Use of Pseudocomponents in Equation-of-State Calculations

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Summary A new method is presented for performing equation-of-state (EOS) calculations with pseudocomponents that are obtained by lumping pure components of a multicomponent reservoir fluid description. The method recognizes that a pseudocomponent represents a mixture of components and thus has the thermodynamic behavior of a mixture, rather than that of a single component. The standard expression for the chemical potential is replaced by an adapted pseudopotential. The method also yields convenient procedures for obtaining phase densities and viscosities. The accuracy of the method is demonstrated by comparing phase splits, lumped mole fractions in liquid and vapor phases, and phase densities and phase viscosities obtained from a lumped fluid description with the same data as those obtained from a fully compositional description of hydrocarbon systems. Generally, deviations are not more than a few percent. The method enables the use of a reduced compositional fluid representation in numerical simulation studies without any essential loss in modeling accuracy.