| abstract |
A cyclic process is described for recovering heavy oil from a reservoir having a network of generally linear, narrow permeable communication channels interconnecting outlying producing wells with an injection well. Except for the channels, the reservoir must be sufficiently impermeable so that pressure may be built up therein by the continued injection of oxidizing gas and propagation of a combustion front when the producers are choked or shut in. The process comprises: (a) initiating combustion in the reservoir at the injection well; (b) injecting oxidizing gas into the reservoir at less than fracturing pressure with the producers open, to propagate a rapid advance of the combustion front through a first channel toward a first of the producers; (c) after heat breakthrough has been established between the injector and said first producer, and before the combustion front arrives at said producer, restricting fluid production from said producer (as by choking or shutting the well in); (d) continuing to inject as before to induce widening of the hot first channel and rapid advance of the combustion front down a second channel toward an open second producer; (e) restricting the second producer after gas breakthrough has been established and before the combustion front arrives at said second producer; (f) repeating (d) and (e) for each of the other producers until all of the producers are restricted; (g) continuing to inject as before to cause a significant pressure build-up in the channel network and surrounding reservoir, said built-up pressure being less than the fracturing pressure; (h) substantially terminating oxidizing gas injection and injecting water into the network to cool it to a temperature below that at which significant coking occurs. (i) opening the producers to blowdown the reservoir; and (j) repeating steps (a) to (i) at least once. Preferably, the network of channels is provided by subjecting the wells to cyclic steam stimulation conducted at fracturing pressure, to create both on-trend and off-trend channels interconnecting a group of wells that make up the focal points of the network. |