The volume of heavy oil and bitumen in the oil sands deposits in Western Canada is similar to that of conventional crude oil in the Middle East. This resource is immense but is difficult and energy intensive to extract because the viscosity of the oil is high, typically over 100,000 to 1,000,000+ cP at original reservoir conditions. Current commercial thermal recovery processes used are Steam-Assisted Gravity Drainage (SAGD) and Cyclic Steam Stimulation (CSS). These methods are both energy intensive, emit significant amounts of carbon dioxide to atmosphere, and use large volumes of water to recover the oil. In this work, the focus is on steam-based gravity drainage processes. It has been demonstrated that operating strategy can be altered to improve SAGD performance but it is not clear how well configuration can be changed to improve recovery, energy intensity, thermal efficiency, water use, and flue gas emissions. This paper examines the impact of position and geometry of steam injectors on the performance of steam-based gravity drainage processes in a heterogeneous reservoir. Different injection well configurations including single horizontal (typical SAGD), offset SAGD, and vertical/horizontal well combinations have been evaluated by using a detailed, three-dimensional, geostatistically-populated, large-scale thermal reservoir simulation model derived from core data examinations of the Dover pilot site. The research reveals how injection well configuration impacts energy delivery to the reservoir, thermal efficiency, and how it changes the evolution of the steam conformance zone and oil flow dynamics in the reservoir. The results suggest that several vertical injectors have the potential to deliver steam more efficiently than a single horizontal injector.
In the province of Alberta, Canada, the volume of oil sands as reported by Energy Resources and Conservation Board (ERCB) is about 2.7 billion cubic meters1. Nevertheless, despite their abundance, these oil sands are very viscous and essentially immobile at reservoir conditions. Currently, most in situ recovery processes used to recover oil sands are steambased. One commercial process is the Steam-Assisted Gravity Drainage (SAGD) method which has been used to mobilize and improve the recovery of oil sands by injecting steam into a horizontal well placed above a horizontal producer2,3,4. There are several SAGD projects currently in operation and being developed in the Athabasca area1. However, variability in performance is large; there are many SAGD wellpairs that have performed with low production rates and thermal efficiency1. This is usually a result of reservoir geology and operating strategy. It is required that SAGD or SAGD-variants are robust, that is, they are geotolerant, so that they can be tuned to operate with reasonable thermal efficiency in geologically-diverse oil sands reservoirs. There are a number of design issues that need to be understood to develop and improve the performance of SAGD. Some examples are well configurations and operating conditions such as steamtrap control and injection pressure. Well configurations and its impact on steam-based gravity drainage processes is the main topic of this paper.
