Sagdox geometry

1. A process to produce bitumen from an at least partially depleted steam-swept bitumen-comprising reservoir:

wherein a reservoir in a natural state containing 100% of a native bitumen has been previously subjected to an initial extraction to produce the at least partially depleted steam-swept reservoir by:

installing a steam assisted gravity drainage (SAGD) system within the reservoir, the SAGD system comprising: a production well having a horizontal distal portion and a vertical proximal portion in communication with an extraction pump; and a steam injection well having a horizontal distal portion above the horizontal distal portion of the production well and a vertical proximal portion in communication with a steam source;

operating the SAGD system, by injecting steam through the steam injection well to the horizontal distal portion thereof into the reservoir with the effect that steam heat and steam pressure are applied to the bitumen thereby reducing viscosity of the bitumen and mobilizing the bitumen to flow downward under gravity drainage; and

extracting bitumen and water from the bitumen-comprising subterranean reservoir into the horizontal distal portion of the production well;

the process comprising:

subjecting the at least partially depleted steam-swept reservoir to a secondary extraction comprising:

installing an oxygenatious gas injection well with a gas outlet in the at least partially depleted steam-swept reservoir above the horizontal distal portion of the production well, the gas injection well being separate from the SAGD system and horizontally spaced apart from the SAGD system;

operating the oxygenatious gas injection well by injecting oxygenatious gas through the gas outlet and igniting the bitumen in a combustion zone in the at least partially depleted steam-swept reservoir with the effect that one of: combustion heat energy; oxygenatious gas pressure; steam heat and steam pressure generated from vaporized water within the at least partially depleted steam-swept reservoir; and combustion gas pressure is applied to the bitumen, thereby reducing viscosity of the bitumen and mobilizing the bitumen to flow downward under gravity drainage into the horizontal distal portion of the production well, wherein a volume to volume ratio of oxygenatious gas in the secondary extraction relative to water used to produce steam in the initial extraction is in the range of 5% to 50%.

2. The process according to claim 1 wherein the initial extraction produces an at least partially depleted steam-swept reservoir having between 10-25% residual bitumen of the native bitumen, and wherein the secondary extraction comprises:

heating the residual bitumen with combustion gases in the combustion zone;

stripping light fractions from the residual bitumen;

pyrolyzing the residual bitumen to produce coke;

oxidizing the coke; and

producing a combustion swept zone having substantially no recoverable bitumen.

3. The process according to claim 1 wherein the ratio is in the range of 10% to 40%.

4. The process according to claim 1 , comprising:

installing a produced gas (PG) extraction well with an inlet within the at least partially depleted steam-swept reservoir, the PG extraction well being separate from the SAGD system and horizontally spaced apart from the SAGD system; and

operating the PG extraction well to extract non-condensable gas.

5. The process according to claim 4 , comprising:

controlling the formation of the combustion zone by controlling one of: the injection of oxygenatious gas; and the extraction of produced gas.

6. The process according to claim 5 , wherein one of: a plurality of oxygenatious gas injection well outlets; and a plurality of PG extraction well inlets, are spaced apart horizontally to control the formation of the combustion zone.