Abstract
The ever increasing world demand for energy to satisfy the current needs and future economic growth has forced the oil and gas industry to exploit challenging energy resources. Heavy oil and oil sands are challenging due to the complexity of the reservoirs together with the high oil viscosities which are often greater than hundreds of thousands to millions of centipoise. Most steam-based recovery processes such as Cyclic Steam Stimulation (CSS) and Steam-Assisted Gravity Drainage (SAGD) require a competent cap-rock to prevent excessive steam losses and maintain good thermal efficiency and production rates. However, there exist significant amounts of oil sand resources which have little or no cap-rock and thus, at this point, these resources are considered inaccessible. This research examines the feasibility of using SAGD in oil sands reservoirs with no cap rock with detailed thermal reservoir simulation. The results of this research provide guidelines on how to implement the SAGD process in shallow oil sands reservoirs with no cap rock. This could unlock a resource that is currently considered inaccessible. The results show that vertical chamber growth can be controlled to some extent by using variable pressure operating strategies and co-injection of a non-condensable gas such as methane. In oil sands reservoirs without cap-rocks, pressure control is critical especially if there is to be minimal fluid invasion from the oil sands formation into the water zone above. However, the pressure must be sufficient to delay or prevent flow of water into the steam chamber. This study is important since in Alberta, Canada alone there are billions of barrels of shallow oil sands resources without sufficient cap rock to operate conventional high pressure steam recovery processes such as CSS and SAGD. The results of the study provide a technical basis to design feasible low pressure steam processes for such reservoirs.
