A Theoretical Investigation Of Forward Combustion In A One-Dimensional System
Authors: Verma Vidya Bhushan , Reynolds Albert C. , Thomas Gordon W. 
Published: December 2007

This paper treats a theoretical investigation of forward combustion in a simulated laboratory combustion tube. To this end, a mathematical model is presented that incorporates the principal kinetic, presented that incorporates the principal kinetic, thermal, thermodynamic and hydrodynamic aspects of the process. The model is similar to those presented by process. The model is similar to those presented by Gottfried and Crookston, et al. except unlike the Gottfried model, we treat seven equations rather than five, and account for a mass balance an fuel, which incorporates both fuel laydown and burnoff. Furthermore, vaporization-condensation of both oil and water is included. Our model differs from the model of Crookston, et al. insofar as we consider some of the ail vapor to participate in combustion. We further differ by employing a more field formulation of the problem at points where liquid phase disappearance occurs rather than using an arbitrary artifice to handle this situation. In addition, we use a sequential implicit solution technique which we found to be satisfactory.

With the exception of the gas phase, mass and heat balances are always maintained within less than 0.5$. We frequently see the same bounds on the gas balances, however, under some circumstances this bound is exceeded. This is expected since the gas saturation is calculated by difference, and thereby reflects the cumulative errors in the computation.

The model yields spatial distributions of pressure, temperature, oil, water, gas, and fuel pressure, temperature, oil, water, gas, and fuel saturations and/or concentrations. In addition, we can determine at any point and time the mole fractions of various components in the gas phase. Finally, it is possible to predict recovery factors, production rates, cumulative production, and instantaneous and cumulative WOR's and gas-liquid ratios.

In this paper, we present a detailed interpretation of the various computed profiles and identify some phenomena the existence of an oil vapor plateau, peak "shaving" of the water vapor profiles, etc.) not previously identified in the profiles, etc.) not previously identified in the literature. Comparisons of the computed results with laboratory experimental results are also presented.

Introduction

Thermal recovery methods are most promising for recovering low API gravity crudes, or oil from shales or tars. Basically the idea is to supply heat to the reservoir to lower the oil viscosity and enhance flow to the production wells. The heat can be generated at the surface, or in-place, and supplied either locally or globally through one or more injection wells. In most applications involving surface generation, steam is the heat medium. In-place generation involves the propagation of a combustion zone to globally affect the reservoir. The latter process is the concern of this mark, in particular forward combustion, which us briefly describe below.

In forward combustion, the crude is ignited in the vicinity of an air injection well followed by continued air injection. Due to the heat, part of the oil ahead of the burning zone is vaporized, and displaced downstream by the incoming hot gases. A residue derived from the heavy ends of the oil is left behind to serve as fuel for the combustion front, This is referred to as cot,. In addition, some of the oil vapors are undoubtedly consumed in the combustion reactions. The displaced oil vapor ahead of the front alternately condenses to form an oil bank, which is driven to the production wells.

In the published literature, initial attempts were directed toward an analytical treatment of the heat flow mechanisms without a consideration of fluid flow effects. Heat transfer inside the system and losses to the surroundings were accounted for by conduction and/or convection. The combustion zone was simulated by incorporating a transient instantaneous heat source in the energy equations. All of these treatments were highly idealized insofar as the reaction kinetics of the process were not taken into account.