Given enormous capital costs, operating expenses, flue gas emissions, water treatment and handling costs spent in thermal in situ bitumen recovery processes, improving the overall efficiency by lowering energy requirements, environmental impact, and costs of these production techniques is a priority. Steam Assisted Gravity Drainage (SAGD) is the most widely used in situ recovery technique in Athabasca reservoirs, steam generation is done on surface and consequently, because of heat losses, the energy efficiency of SAGD can never be ideal with respect to the energy delivered to the sandface. An alternate to surface steam generation is by In Situ Combustion (ISC) where heat is generated within the formation through injection of air at a sufficiently high pressure to initiate combustion of bitumen. In this manner, the heat from the combustion reactions can be used directly to mobilize the bitumen. As an alternative, the heat can be used to generate steam within the formation which then is the agent to move heat in the reservoir. In this research, alternative hybrid techniques with simultaneous and sequential SAGD-ISC processes are examined to maximize the thermal efficiency of the recovery process. These hybrid processes have the advantage that during ISC, steam is generated within the reservoir from injected and formation water. This implies that surface requirements for surface steam generation are lower and if there is in situ storage of combustion gases, that overall gas emissions are reduced. Detailed, three-dimensional reservoir simulations are done to examine the dynamics of hybrid SAGD-ISC processes to enable design of these processes.
Two requirements of in situ heavy oil recovery processes must be honored for successful performance: first, make the heavy oil or bitumen mobile, and second, move the mobilized oil to a production well. Since virgin viscosities of Athabasca bitumen generally exceed several million cP, the key to success is first measured by the process' ability to mobilize the heavy oil or bitumen. There are four main methods to do this: heat, solvent dilution, solvent deasphalting, and in situ upgrading. An alternative source of heat is in situ combustion which also provides combustion gases that could potentially help to move mobilized bitumen in the reservoir.
In thermal recovery, the reservoir flow resistance is reduced by lowering the viscosity of the crude oil by using heat. Thermal recovery processes used belong to two main classes: those in which a hot fluid is injected into the reservoir and those in which heat is generated within the reservoir itself. Steamassisted gravity drainage (SAGD) falls into the first category. On the other hand, In-Situ Combustion (ISC) involves the propagation of an energy generating oxidation zone within reservoir. At certain pressure and temperature conditions, injected oxygen reacts with a fraction of the oil in the reservoir and generates heat and gas that mobilizes oil and drives it to production wells1. There have been several in situ combustion pilot projects in bitumen reservoirs: Marguerite Lake and Whitesands2,3 are examples.