Numerical simulation of the insitu combustion process is complicated by sharp gradients, with different temporal and special regimes applying to the reaction front and diffusional transport. It is not possible to achieve fine scale solutions at field scale in a reasonable time, owing to the onerous computer requirements. Instead, grid coarsening procedures were used. Simulation solutions were obtained for a homogeneous reservoir section of the THAI® field pilot, near Conklin, Alberta, Canada. The reservoir model did not include an interbedded shale layer, or bottom water layer, and the study therefore represents a non-optimal, first stage simulation of the THAI process, prior to incorporating more reservoir complexities. The results show that the process is inherently stable over a six year operating period, since there was no oxygen in the produced gas. High temperatures are generated in the narrow combustion front zone (900 °C) but 60 m ahead the temperature is 500 – 600 °C. Rapid desaturation of reservoir water takes place ahead of the combustion front, allowing combustion gases to enter into the colder bitumen layers, thereby creating some oil mobility. Of particular significance, is the existence of a narrow, high saturation, Steam Zone, extending to more than 15 m, and up to 30 m during later stages of production. The steam zone propagates at up three times faster than that of the combustion front. Also, the Mobile Oil Zone (MOZ) is very significant characteristic of the THAI process throughout the whole production period. However, the temperature in the MOZ, close to the horizontal producer well, is quite low, around 150–180 °C. The oil recovery factor was approximately 60 % in the zone swept by the gas-steam front. Oil production peaked at 69 m3/day rate, averaging 350 barrrels per day for the single well pair.

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