Reverse Combustion - A New Oil Recovery Technique

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Abstract
Although the broad recovery method known as underground combustion embodies many related techniques, principle attention has been focused on alternatives known as "forward" and "reverse" combustion. Summaries follow in this issue for three Technical Publications on reverse combustion, and it is the purpose of this article to briefly review in situ combustion and to introduce the subject of reverse combustion. Secondary recovery by underground combustion is a most intriguing method which provides energy and material transport through porous media. The "heat wave" effectively reduces the viscosity of the driven oil and thus, for many crudes, dramatically increases its fluidity. The material transport ahead of the heat wave acts as a miscible fluid drive. The result is a very efficient sweep of residual oil from the area. Our fundamental knowledge about the process is limited, however, except in a general way; thus, detailed engineering recommendations are difficult. It must be remembered that exceedingly complex cases of multiphase fluid flow, multi-dimensional and multi-mechanistic heat transfer, heterogeneously catalyzed reaction kinetics, and multi-component phase equilibria are all combined in this process in a mutually dependent manner. It is no wonder that our scientists have barely scratched the surface in understanding the in situ combustion process. Both forward and reverse combustions utilize as fuel the residual coke from the in-place oil. The difference between the techniques is whether the flame front and material flow are in the same direction (forward combustion) or in opposite directions (reverse combustion). A simple analogy may be used to clarify the difference. Picture yourself smoking a cigarette in the conventional manner. The flame front and the products of combustion both travel toward your mouth (forward combustion). If you blow into the cigarette, however, the products of combustion travel outward while the flame front still moves toward your mouth (reverse combustion). Thus, in forward combustion both oil and the heated zone are moving toward the producing well and away from the injection well, while in reverse combustion the flame front moves away from the producing well.

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