Tie-simplex method for thermal-compositional simulation

Advisor

Hamdi Tchelepi, primary advisor
Franklin Mattes Orr, Jr., advisor
Denis Voskov, advisor

Abstract

Enhanced Oil Recovery (EOR) processes usually involve complex phase behaviors between the injected fluid (e.g., steam, hydrocarbon gas, CO₂) and the in-situ rock-fluid system. Equation-of-State (EoS) computations for complex mixtures than can form three, or more, phases at equilibrium pose significant challenges. In addition, issues related to proper coupling of the thermodynamic phase-behavior with multi-component transport across multiple fluid phases must be resolved in order to model the behaviors of large-scale EOR processes accurately and efficiently. Here, we propose an EoS-based tie-simplex framework to deal with the thermodynamic phase behavior, in which an arbitrary number of phases can form. It is shown that our generalized negative-flash method yields the unique tie-simplex parameterization of the compositional space. Specifically, we show that the tie-simplexes change continuously as a function of temperature, pressure, and composition. In the course of a thermal-compositional simulation, the compositional space is tabulated adaptively using tie-simplexes. We also prove that the Gibbs free-energy analysis of this tie-simplex space is equivalent to conventional methods for equilibrium phase calculations. This multiphase tie-simplex method is integrated into Stanford's General-Purpose Research Simulator (GPRS), and its application to thermal-compositional simulation is demonstrated here using several challenging thermal-compositional flows with complex phase behaviors.