In-situ combustion is a subject of continuing interest due to itsrnrich interplay of flow, mass/heat transfer and reactions. Thernprocess complexity, however, has precluded its thoroughrnunderstanding. In this paper, we provide some analyticalrnresults and pore-network simulations that explore fundamentalrnaspects of this process.rnThe analytical approach relies on high-activation energyrnasymptotics. It consists of the assumption that the combustionrnfront is a thin layer, within which reactions occur. We reviewrnour recent findings and derive exact results for the frontrntemperature, the front propagation velocity and oxygenrnconsumption. The results are then compared to pore-networkrnsimulations, where the effects of pore structure are included inrna detailed simulation at the pore-network level. Thernsimulations demonstrate the validity of the thin layerrnassumption and provide approaches for upscaling.rnThen, the effect of porous medium heterogeneity, arnubiquitous feature of oil reservoirs, on the front is considered,rnin particular, in the form of a layered reservoir system. Thernfronts in two layers can be coupled under certain conditions,rndepending on the permeability-thickness contrast R betweenrnthe layers, the extent h of external heat losses and the inletrnconditions. We derive the parameter space, where thisrncoupling occurs, and compare the results with the pore-networkrnsimulations. Stability of the derived stationaryrnnonequilibrium states is also analyzed. It is shown that thernadiabatic states are always stable; whereas the non-adiabaticrnstates being conditionally stable. This suggests that coherencernof the fronts in the layered system is possible under certainrnconditions and that the effect of heterogeneity is not asrndetrimental to the process and its sweep efficiency, providedrnthat heterogeneity does not exceed a certain limit, Rc.
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