Comprehensive Enthalpy-Based Phase Behavior for EOS-Based Compositional Thermal Simulation

Abstract

Abstract This work presents the selection of the most adequate isenthalpic flash method for EOS-based compositional thermal simulation. Five multi-component isenthalpic flash methods were studied. We consider water as a component and the mutual solubility of water and hydrocarbons. A novel isenthalpic flash method is presented. We present a new single-component isenthalpic flash. Finally, we propose a new phase identification algorithm for application into thermal EOR processes. Five multi-component isenthalpic flash methods were studied: direct substitution, full Newton, partial Newton, Q-function maximization, and a novel bisection-like isenthalpic flash. Modifications to Q-function maximization are proposed to account for cases in which isothermal flash could fail. We compared these methods for robustness and computational performance to select the most adequate for compositional thermal simulation. A new isenthalpic flash for single-component fluids is proposed and compared with more traditional solutions such as steam tables. Finally, we present a new method for phase identification for thermal EOR processes based on fluid enthalpy and mass density. We compare five multi-component isenthalpic flash methods using two different initial conditions. We perform a series of flash calculations over a pressure and enthalpy range. More than 179000 flash calculations were performed for each method. Also, we compare the combined use of the methods studied. The methods were evaluated in terms of robustness and performance. From the individual method comparison, we conclude that none of the methods studied by themselves is adequate for thermal reservoir simulation. However, the combined use of these methods shows better results. We found when we use both Newton methods and call Q-function maximization with bisection when Newton fails to be robust enough for its application to compositional thermal reservoir simulation. We show a case of the single-component isenthalpic flash method using water and comparing it with steam tables. The results are in good agreement. The method proposed in this work has the advantage that could be applied to any component described by an equation of state. The results of the phase-identification algorithm are shown, demonstrating its usability for compositional thermal reservoir simulation.