Regional Stratigraphic Framework and Outcrop-Subsurface Correlation, Athabasca Oil Sands, Fort McMurray Area, Alberta

Darrell K. Cotterill
Parallax Resources Ltd, Spruce Grove, AB

Most of the bitumen in the Athabasca oil sands is within the Lower Cretaceous McMurray Formation and Wabiskaw Member of the Mannville Group. Identification and mapping of regionally correlatable surfaces within the Surface Mineable Area (SMA) gives a three-dimensional picture of various structures that influence reservoir development of the oil sands in the subsurface.

Current core control is excellent in regions of enhanced exploitation within the SMA. A grid of cross-sections were constructed, tied to available core data, and integrated with nearby outcrops. The regional Devonian Prairie Evaporite Salt-Dissolution Front affected sedimentation and reservoir development, pre- during-, and post-Wabiskaw/McMurray deposition. Main influences were on regional shifts in relative base level, development of regional erosional surfaces and effects of this erosion on preservation potential. Some of the local sedimentological effects related to salt-withdrawal tectonics include: the development of bay-fills, orientation of channels, preservation of barrier, back-barrier, marsh and tidal flat deposits. Within paleo-low structures, local karst/marls, vertical accretion abandonment fills, back-barrier bay-fills and coals are preserved.

Major differences between the SMA and the in-situ area to the south include: an absence of regional mudstone seals, with the associated overlying coarsening-upward parasequences; a more marine character to the overall succession, with development of barrier complexes and local firmgrounds. In the SMA the Wabiskaw-McMurray deposit shows extreme lateral facies variation, and combined mining and in-situ development of bitumen resources in such areas require a clear understanding of the 3-D stratigraphic and sedimentological framework.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005