A New Splitting Scheme and Existence of Elliptic Region for Gasflood Modeling

Abstract

Summary Analytical models of gasflooding are important for enhanced-oil-recovery (EOR) screening, for interpretation of laboratory data, and for streamline modeling. Introduction of two Lagrangian coordinates linked with one of the components and with the overall two-phase flux results in splitting the compositional model into an auxiliary system and an independent scalar equation. The number of equations in the auxiliary system is less by one if compared with the compositional model, making analytical modeling possible for more practical cases. The auxiliary system contains only thermodynamic functions and is independent of transport properties. Therefore, phase transitions and minimum miscibility pressure for gas injection are also independent of transport properties. The new splitting method is applicable for both self-similar solutions of continuous gas injection and nonself-similar solvent-slug problems. Analytical solution for four-component oil displacement by a nitrogen-based solvent was obtained using the splitting technique. The compositional two-phase model contains an elliptic region if and only if an elliptic region is also present in the auxiliary system. Calculations for several four-component mixtures exhibit existence of an elliptic region in compositional modeling.