Use of a Reduced Method in Compositional Simulation

Simulating gas injection processes requires a compositional model to predict the fluid properties resulting from mass transfer between reservoir fluid and injection gas. A drawback of compositional simulation is the efficiency and robustness of phase equilibrium calculations. Reduced methods for phase equilibrium calculations have been studied as a potential solution to improve the efficiency of compositional simulation. However, most of those studies have been performed only in stand-alone calculations, and the robustness and efficiency of a reduced method has not been confirmed in compositional simulation. In this research we develop a robust and efficient algorithm for a reduced method and validate it in compositional simulation. We examine the efficiency and convergence property of the conventional algorithm for a reduced method, and solve several implementation problems in a compositional simulator. The reduced method is implemented in UTCOMP, a compositional IMPEC simulator, to demonstrate the performance for various numbers of components and degrees of miscibility. The results show that the reduced method enables significant saving in execution time of compositional simulation without loss of accuracy, compared to standard methods. Also, we observe that the reduced method exhibits improved robustness especially for miscible processes where composition paths go near critical regions.