A succession-of-states model for the in situ combustion process

A two-dimensional succession-of-states multifront tracking model was developed for the in-situ combustion enhanced oil recovery process. The model approximates the flow domain in the reservoir as a series of regions separated by sharp fronts and places the primary computational effort on tracking the movement of these fronts. Flow is approximated as a succession of steady states based on incompressible fluid flow. This formulation leads to a set of Poisson equations (one for each region) coupled by exterior and frontal conditions. Exterior conditions are imposed by reservoir geometry and well histories. Frontal conditions are dictated by conservation of mass and energy and pressure continuity at the fronts separating regions. The resulting system of equations is solved by a finite element method, used because of its inherent ability to accommodate non-orthogonal domains and a grid redistribution scheme that matches fronts to element boundaries.;Several validation runs were performed comparing the results of the model with analytical solutions for particular problems, available data in the literature, and results from a commercial simulator. The model appears to provide accurate, dispersion-free numerical solutions with relatively small computational time. The usefulness of the model for simulating effects of viscous and gravitational forces, chemical reactions, and fluid condensation is demonstrated. This model has the potential to inexpensively simulate field-scale thermal recovery processes such as in-situ combustion or steam drives in heterogeneous reservoirs.