A field study by compositional simulation results in expensive computation by a huge number of phase equilibrium calculations. The common method of reducing the computation time is to describe the fluid by lumping its components into several pseudo-components. The main drawback of pseudoization is the loss of detailed compositional information on reservoir fluids.

This paper reports results of evaluation studies on accuracy and efficiency of different computing methods of equation-of-state incorporated in a compositional simulation model. The compositional model was formulated by the IMPES approach. The computation methods used for iterative EOS flash calculations are the successive substitution iteration (SSI) method, Newton method, their combination, and a generalized Michelsen method to reduce the number of independent variables.

Performances of the flash computation methods were evaluated by simulating behavior of a single well in gas condensate and volatile oil reservoirs, where the reservoir fluids were grouped into 5, 10, and 16 pseudo-components for each reservoir. Simulation demonstrated high effectiveness of the parameter reduction method showing significant decreases in flash computation time compared to the conventional methods, particularly when the number of pseudo-components was increased.

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