A Comprehensive Approach to In-Situ Combustion Modeling

Abstract

ABSTRACT Low temperature oxidation (LTO) has long been recognized as one of the dominant mechanisms controlling fuel availability in in-situ combustion. Its effect on the physical properties of crude oils is also well known. In spite of these findings, the prevailing conceptual model of in-situ combustion still hinges on thermal cracking (in isolation) ahead of the firefront, to provide sufficient fuel (coke) for propagation of the reaction zone. Previous simulation studies, which purported to include LTO as part of the reaction scheme, have unrealistically specified the reaction products as carbon oxides and water. Furthermore, oil compositional changes due to oxidation have been completely neglected. This paper describes a unified pseudo-mechanistic reaction model for mathematical modeling of in-situ combustion of Athabasca bitumen. The model represents a consolidation of individual experimental kinetic studies on thermal cracking and low temperature oxidation of Athabasca bitumen, and reported data for the high temperature oxidation of coke. The formulation is comprehensive in that it allows bitumen to undergo density and viscosity increases, as well as reduced reactivity to oxidation, with increased oxidation extent. Hydrocarbon bypassing due to quenching of the combustion front is also permitted with the proposed kinetic model. The paper includes application of the reaction model in numerical simulations of adiabatic combustion tube tests performed on Athabasca bitumen. A significant feature of the model is its ability to predict the dual oxidation uptake peaks associated with ramped temperature oxidation experiments.