Abstract

A mathematical model has been developed to simulate the flow of oil water and gas and heal: transport in a heavy oil reservoir during a combustion process. The model accounts for conduction and convection in the reservoir and instantaneous heat generation by combustion at a moving front, as well as, heat losses to cap and base rocks by conduction. In the model, the energy equation is first solved by the implicit technique to obtain temperature distribution following the burning of a block at a given injection rate. For pressure and saturation calculations. small time steps are used to obtain stable solutions of the non-linear, partial differential equations for the flow of gas, water and oil using the IMPES method.

The model has been applied to study the injection and production performance of a combustion pilot in operation for about ten years in a heavy oil reservoir in the Lloydminster area. Predicated well pressures and oil production rates agree with the reported field data. The model shows that gas drive is one of the main oil recovery mechanisms associated with the fire flood process in a relatively thin heavy oil reservoir.

Based on the oil recovery mechanism identified, the model was employed to investigate the effects of oxygen content, air and water rates, and fuel concentration on oil production in a given reservoir. The model also was used to study the effects of formation thickness and fluids saturations on the expected fire flood performance. From these sensitivity analyses, the optimal air injection rate and oxygen content can be determined for a given reservoir.

Introduction

Considerable progress has been made in recent years in simulations of in-situ combustion processes, Comprehensive models have been developed by Coats (1), Crookston, et a1. (2). Huang, et a1.(3), Rubin Bnd Vinsome (4), Youngren (5), and others to simulate flew of fluids and heat transfer in porous media during a combustion process. Reports of kinetic studies of the combustion or oxidation reactions also are available as discussed by Fassihi, et al. (6) and other investigators. Unfortunately, there are many uncertainties regarding mechanisms of oxidation (combustion) reactions between hydrocarbon fuels and oxidants in porous media, a key feature in any combustion process. The chemical reactions may take place in homogeneous phases in vapor or liquid, or in heterogeneous systems between solid-liquid, gas-solid or gas-liquid interfaces. Roles played by constituents of the fluids or rocks in the porous media 1n catalyzing the reactions are not well understood. Temperature distributions during the combustion, therefore, cannot be predicted with great confidences because of these uncertainties. These, in turn, affect results calculated for pressure and saturation profiles, and production performances.

Because of the difficulties discussed above, this work was undertaken with the main objective of developing a simple model for firefloods in thin reservoirs containing heavy oils. Such a model can be utilized to investigate effects of reservoir and fluid properties and various operating parameters on the injection and production performances.

This content is only available via PDF.
You can access this article if you purchase or spend a download.