- Copyright © 2002 Society of Exploration Geophysicists
The Athabasca oil sands in western Canada are one of the largest hydrocarbon accumulations in the world. Due to the low viscosity, special production techniques have to be applied to extract the oil. One extraction technique is steam-assisted gravity drainage (SAGD) which has a simple concept. An upper horizontal well injects steam into the producing zone, creating a high-temperature steam chamber in the formation. The heat melts the thick crude and allows it to flow more freely, with gravity's asistance, to the horizontal production well, which is parallel to and 4–6 m below the injection well.
For efficient oil recovery, the horizontal injection and production wells must be optimally placed. Changes in lithology, the presence of laterally continuous shale stringers, or faults can hamper the free flow of oil and reduce productivity significantly. Consequently, the subsurface must be well understood.
The primary tool for this investigation is the analysis of data from wells drilled into the reservoir to test stratigraphy. However, for economic reasons these wells can only be drilled at a certain spacing. Seismic data can help resolve the reservoir characteristics between these wells.
The object of this study is to resolve the reservoir quality—i.e., to analyze sand/shale deposition with seismic tools.
The study area is PanCanadian's Christina Lake Thermal Project in northeast Alberta. The heavy-oil-prone reservoir zone is McMurray Formation in the lower Cretaceous. The depth of this zone is approximately 400 m.
At Christina Lake, McMurray Formation can be divided into three units with a total thickness of about 80–90 m. The lower unit is frequently below the water contact. The middle McMurray is a series of stacked estuarine channel sands with excellent reservoir quality and porosity often in excess of 35%. The upper McMurray was deposited as tidal shoreline or bay bars. Furthermore, an upper McMurray …