Since it was discovered in the early 1900's, several improvements have been suggested for the in situ combustion technology. Top-down combustion displacement, is a process proposed for application with horizontal well technologies. In this configuration, air is injected near the middle of the reservoir, close to the overburden, through a horizontal well or a number of vertical wells. Fluids are produced from the reservoir through another horizontal well placed near the bottom of the reservoir. In this configuration, the combustion front moves downward in the gravity direction and displaces fluids to the production well.

Combustion front formation and its stability are major concerns in this arrangement. While the short distance between injector and producer addresses the cold oil blocking problem in the reservoir, it has the potential to create air fingers which could prevent stable advance of the combustion zone in a horizontal plane. Front self-correction must occur to prevent oxygen from fingering to the production wells.

To prove this idea, experiments at reservoir pressure were carried in a two-dimensional SAGD model with Athabasca bitumen. Air was injected into the SAGD steam chamber, from the middle, and fluids were produced from the bottom. Front advancing directions were monitored by a series of thermocouples located inside the model. It was found that combustion zone starts spreading horizontally in the model until it reaches a limiting point then it starts moving downward as a horizontal front. Despite heterogeneity of the oil saturation and relative permeability in the steam chamber and un-swept zones, the combustion front moved almost as a horizontal plane and no sharp fingers were recorded in the experiments. These experiments show that stable middle-down combustion is feasible.

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