The reverse combustion method can be applicable, in principle, to ultra heavy oils as an EOR method. However, the low recovery efficiency of the reverse combustion method, as is known, seems to dismiss this advantage. As a part of research work for improving the recovery efficiency by the reverse combustion method, it was intended, first of all, to investigate general behaviors of the reverse combustion through combustion tube experiments, because very few works in this area had been done. And the influence of oxygen injection rate was investigated as a first part. Results are summarized as follows. (1) In the reverse combustion, the combustion zone can be maintained at a temperature lower than 400°C that is the critical temperature in the forward combustion. This means that the fuel in the reverse combustion is not a cork but light components of oil. (2) The temperature of combustion zone increases as the injection rate of oxygen increases. (3) The propagation speed of combustion front increases with the oxygen injection rate. (4) There is an optimum injection rate of oxygen to obtain a maximum recovery. (5) The maximum recovery in the reverse combustion of a partiucular crude oil of 0.938 in specific gravity was 58%, whereas that in the forward combustion was 90%.
Laboratory experiments on the reverse combustion were carried out to investigate the fundamental phenomena in a reservoir and the influence of reservoir conditions on the overall behavior of fireflooding, with the aim of the application for improving oil recovery. Results are summarized as follows. (1) Since cork formed by the thermal decomposition is the fuel in a forward combustion, the forward fireflooding would not be applicable unless oil density is high enough. However, there is no limitation of oil density in the reverse combustion, because light components, perhaps in a gas phase, burn as fuel. (2) The heat transfer to a low temperature region ahead of the combustion front and the heat generation by the combustion are competitive mechanisms for controlling the temperature of the combustion zone. Therefore, the heat transfer coefficient of the reservoir ahead of the combustion front is one of the most important factors affecting the whole behavior in the reservoir. (3) Oil recovery through the reverse combustion experiments at the present study was 40 to 60%, whereas that of the forward combustion experiments at previous studies was ca. 90%. It was decreased as the oil density and/or the reservoir pressure increased.