Analysis of Compositional Models for Laboratory Scale In-Situ Combustion Simulation

Abstract

Summary We study compositional, thermal and reactive flow in porous media and the numerical simulation of those processes, with a focus on laboratory scale In-Situ Combustion (ISC) cases. We discuss the governing equations and models, our numerical framework and its implementation, as well as a two-step verification process using state-of-the-art industrial codes and a grid convergence study. First, we go over a numerical verification process using two industrial codes as well as internal grid-convergence studies. We illustrate that our framework is robust and accurate on complex thermal, compositional and reactive cases. We then investigate the appropriateness and performance (in terms of both runtime and non-linear iterations) of some of the models typically used for compositional and isothermal simulation. We illustrate that in the presence of strong thermal effects, we need to make sure that we can capture the relevant physics using those models. More specifically, we discuss our findings on compositional and thermal models for heat capacity, enthalpy and phase behavior in the context of laboratory scale in-situ combustion. We show that a free-water flash captures the right behavior for our low pressure, high temperature conditions, even in a K-value form. The computational cost is three times lower than using a full flash and two times lower than using a regular K-value flash. Using a temperature-independent heat capacity model, as is often done in the thermal literature, will lead to issues to capture the ignition by overestimating heat capacity at low temperature. We discuss the different options to compute enthalpy in a compositional, thermal setting and show some possible unphysical behavior.