Analytical Modeling for Two-Phase EOR Processes: Splitting Between Hydrodynamics and Thermodynamics

Abstract

Compositional models describe chemical flooding and gas-based IOR processes. It is possible to show from the known analytical solutions of multicomponent polymer/surfactant flood, that the concentration “part” of the solution is completely defined by adsorption isotherms and does not depend on relative permeability and phase viscosities. Analytical models for 1-D displacement of oil by gas have been developed during last 15 years. It was observed from semi-analytical and numerical experiments that several thermodynamic features of the process (MMP, key tie lines, etc) are independent of transport properties. In this paper, we introduce potential coordinates that allow for splitting of the compositional model into a thermodynamics auxiliary system and one transport equation. The number of auxiliary equations is less than the number of equations in the compositional model by one. Explicit projection and lifting procedures are derived. The splitting is valid for either self-similar continuous injection problems or for non-self-similar slug injection problems. Analytical models for displacement of oil by a polymer slug and for oil displacement by rich gas slug with lean gas drive were developed by the splitting procedure. With respect to 3-D flows, splitting takes place only for the case of constant total mobility.