Simulation of an in situ combustion process (ISC) was done for a fractured system at core and matrix block scales. The aim of this work was to: 1) To predict the ISC extinction/propagation condition(s), 2) understand the mechanism of oil recovery and provide some guidelines for ISC upscaling for a fractured system. The study was based on a fine grid, single porosity, multi-phase and multi-component simulation using a thermal reservoir simulator. The following results were obtained:
a) Firstly the simulator was validated for 1-D combustion using the corresponding analytical solutions. 2-D combustion was validated using experimental results available in the literature. It was found that the grid size should not be larger than the combustion zone thickness in order the results be independent of grid size. b) ISC in fractured system was feasible under certain conditions: The extinction/propagation of ISC was strongly dependent on the oxygen diffusion coefficient while the matrix permeability played an important role in oil production. c) Effect of each production mechanism was studied separately whenever it was possible. Oil production is governed mainly by gravity drainage and thermal effects; possible pressure gradient generation in the ISC process seems to have a minor effect. d) The nature of ISC at core scale was different between a single block and multiple blocks (oil production rate, saturations distribution, shape of the combustion front). The characteristics of different zones (i.e. combustion, coke, oil) at block scale were studied and some preliminary guidelines for usscaling are presented.