In-Situ Combustion Model

This paper describes a numerical model forsimulating wet or dry, forward or reverse combustionin one, two, or three dimensions. The formulation isconsiderably more general than any reported to date.The model allows any number and identities ofcomponents. Any component may be distributed inany or all of the four phases (water, oil, gas, andsolid or coke.The formulation allows any number of chemicalreactions. Any reaction may have any number ofreactants, products, and stoichiometry, identifiedthrough input data. The energy balance accounts forheat loss and conduction, conversion, and radiationwithin the reservoir.The model uses no assumptions regarding degreeof oxygen consumption. The oxygen concentration iscalculated throughout the reservoir in accordancewith the calculated fluid flow pattern and reactionkinetics. The model, therefore, simulates the effectsof oxygen bypassing caused by kinetic-limitedcombustion or conformance factors.We believe the implicit model formulation resultsin maximum efficiency (lowest computing cost), andrequired computing times are reported in the paper.The paper includes comparisons of model resultswith reported laboratory adiabatic-tube test results.In addition, the paper includes example field-scalecases, with a sensitivity study showing effects on oilrecovery of uncertainties in rock/fluid properties. Introduction Recent papers by Ali, Crookston et al., andYoungren provide a comprehensive review of earlierwork in numerical modeling of the in-situcombustion process.The trend in this modeling has been toward morerigorous treatment of the fluid flow and interphasemass transfer; inclusion of more components, morecomprehensive reaction kinetics, and stoichiometry;and more implicit treatment of the finite differencemodel equations.The purpose of this work was to extend thegenerality of previous models while preserving orreducing the associated computing-time requirement.The most comprehensive or sophisticated combustionmodels described to date appear to be thoseof Crookston et al. and Youngren. Therefore, wecompare our model formulation and results here withthose models.A common objective of different investigators'efforts in modeling in-situ combustion is developmentof more efficient formulations and methods ofsolution. This is especially important in thecombustion case because of the large number ofcomponents and equations involved. For a given numberof components and reactions, computing time pergrid block per time step will increase rapidly as theformulation is rendered more implicit. However, increasing implicitness tends to allow larger timesteps, which in turn reduces overall computingexpense. To pursue the above objective, then, authorsshould present as completely as possible the details oftheir formulations and the associatedcomputing-time requirements.The thermal model described here simulateswet or dry, forward or reverse combustion in one, two, or three dimensions. The formulation allowsany number and identities of components and anynumber of chemical reactions, with reactants, products, and stoichiometry specified through input products, and stoichiometry specified through input data. SPEJ P. 533