An Experimental Investigation of In-situ Combustion in Heterogeneous Media

Abstract An extensive literature exists on the nature of the reactions that occur when air comes in contact with crude oil during in-situ combustion (ISC); however the effect of reservoir heterogeneity on the ISC process has not been experimentally addressed in prior studies. This paper presents the results of recent experimental efforts to shed more light on ISC. We probe the effect of pressure, temperature, injection flow-rate, and matrix properties on the combustion of a Middle-Eastern 19.7° API oil in a tight-formation sand. The experimental perspective includes both oil oxidation kinetics and combustion-front dynamics in a 1-m long combustion tube. Most importantly, geological effects on the ISC process are investigated by incorporating various degrees of porous medium heterogeneity in the combustion tube runs. From the experimental data, pre and post burn CT scans of the combustion tube, and postmortem analyses, we deduce the effect of both small and large-scale heterogeneities on the spatial and temporal propagation of the combustion front. Specifically, kinetic runs show typical ISC behavior consistent with oxidation and good reactivity of the oil-rock system. It was observed that the supply pressure, injection flow-rate, the reservoir matrix and a metallic additive significantly affected the performance of this particular system. Better combustion resulted from greater oxygen partial pressures and by using the reservoir rock as compared to an artificial sand-clay mix. The combustion tube runs indicate that the process of in-situ combustion can be successfully implemented in a reservoir with small-scale heterogeneities (a few inches) and may be challenged by much larger scales (feet).