| 摘要 |
A method for recovering viscous oil from a subterranean, viscous oil-containing formation by initiating an in-situ combustion operation in the formation using a mixture of oxygen and an inert gas having a low oxygen concentration, preferably about 21 vol. %. After a predetermined period of time, the oxygen concentration is increased to a predetermined higher level, preferably within the range of 95 to 99.5 vol. %. Once the oxygen concentration has reached the desired value, water may be simultaneously injected continuously or intermittently. After a predetermined period of time, produced combustion gas enriched in carbon dioxide separated from the produced oil is compressed and recycled as a diluent for the injected oxygen in place of the inert gas. Thereafter, wet in-situ combustion operation is continued and the oxygen concentration of the injected mixture of oxygen and combustion gas diluent is maintained at a predetermined value so that the concentration of oxygen in the produced combustion gas is maintained at a predetermined value low enough to avoid the danger of an explosion or burning of the production well. After a predetermined period of time, injection of oxygen is terminated and injection of produced combustion gas and water is continued until the combustion front in the formation is discontinued. Finally, water is injected to scavenge heat in the formation. In-situ combustion may be initiated using air followed by injection of a mixture of oxygen and an inert gas having a predetermined oxygen concentration greater than air, preferably 95 to 99.5 vol. %.
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