The process of Steam Assisted Gravity Drainage or better known by its English acronym as SAGD has been successfully tested and commercially implemented in the last decade. It has been particularly successful exploiting the Athabasca oil sands in Alberta. Some of the reservoir features that are frequently present in the oil sands include the presence of bottom water, top water and gas caps. All of them, representing potential thief zones and are inherent to the reservoir nature.
Characterize and understand how those features affect the SAGD process is a key element of early project planning. In the present study, a simulation work to asses the feasibility of SAGD process for a typical section of the McMurray Formation in Alberta was conducted to asses the impact of the mentioned reservoir features.
This study confirms that the presence of bottom water is harmful to the SAGD process; thicker bottom water will be more detrimental. A vertical separation of 5 m to the bottom water was determined as optimum for the production well in order to achieve better recovery and economics. Depleted gas pools associated, or in partial communication with bitumen reservoirs represent a potential risk to the effectiveness of SAGD. The connectivity of gas pools to bitumen reservoirs depends on the vertical permeability and thickness of the material that lay in between; this determines their potential to prevent steam to escape up to depleted gas caps. An optimal range of inter-well spacing among 50 m and 80 m was established for the average reservoir conditions evaluated in this study.