Oil Sands of Canada: Geologic Framework and Influence of Regional Salt-Dissolution Effects

Hein, Fran¹ (1) Alberta Energy and Utilities Board, Calgary, AB

Canadian oil sands cover an area > 140,000 square-km in northeastern Alberta. The Cretaceous lower Mannville Group host sediments include: the Wabiskaw-McMurray for Athabasca; the Bluesky-Gething for Peace River; and the younger, Grand Rapids – Clearwater for Cold Lake. Structure associated with the regional salt-dissolution front mainly affected Athabasca and Cold Lake, whereas controls at Peace River relate to the sub-Cretaceous unconformity. Influences of the salt-dissolution front included creation of extensive N-NW valley systems for the main Athabasca; E-W for eastern and southern Athabasca; and two superimposed N-S and NW-SE incised valley systems for Cold Lake. Other salt-dissolution effects in Athabasca and Cold Lake relate to the development of more regional bay-fill deposits outside of the main incised valleys; local karstification and development of thick, organic and deltaic successions. At Peace River controls on the NE-SW incised valleys relate to paleotopographic effects, largely due to erosion on the sub-Cretaceous unconformity. Other post-depositional effects for oil sands include: development of salt ‘roll-over' and anticlinal structures, younger paleokarst, and local faulting, all of which resulted in combined stratigraphic-structural traps for much of the bitumen and associated water and gas reservoirs. Enhanced accommodation at Peace River allowed for the vertical and lateral separation of reservoirs; whereas more reduced accommodation at Athabasca and Cold Lake resulted in superimposed, inherently complex reservoir interconnections. Integration of regional geologic frameworks with local depositional features of the different oil sands deposits allows for efficient development of these vast resources.