In-situ combustion (ISC) is an intriguing yet complex method of enhanced oil recovery due to the interplay of air flow and oil reactivity. This paper presents the results of a recent experimental effort to shed more light on the ISC process by investigating the effects of different scales of porous medium heterogeneity on ISC. We probed the effects of pressure, temperature, injection rates and matrix properties on the combustion of Middle-Eastern 19.7° API and a Californian 16° API crude oils. The experimental perspective includes both oil oxidation kinetics and combustion-front dynamics in a 1-m long combustion tube. After establishing successful combustion in homogeneous media, we proceeded to investigate the effect of heterogeneity on the ISC process by conducting combustion tube runs in a gravity-stable mode. From the experimental data, pre and post-burn CT scans, and postmortem analysis, we deduced the effect of both small and large-scale heterogeneities on the spatial and temporal propagation of the combustion front. The combustion front traveled unhindered through sections of the combustion tube containing heterogeneous packing with length scales on the order of centimeters. On the other hand, it was more difficult to obtain successful front propagation in media with heterogeneities on the order of tens of centimeters. The ISC process was probably challenged by the relatively fast transport of air through high-permeability zones and the relatively slow transport of the much-needed air through low permeability sandstone thereby effectively starving the burning front of oxygen, and extinguishing the process in this case.

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