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Source rock contributions to the Lower Cretaceous heavy oil accumulations in Alberta: a basin modeling study

American Association of Petroleum Geologists Bulletin

By:
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DOI: 10.1306/11141111064

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Abstract

The origin of the immense oil sand deposits in Lower Cretaceous reservoirs of the Western Canada sedimentary basin is still a matter of debate, specifically with respect to the original in-place volumes and contributing source rocks. In this study, the contributions from the main source rocks were addressed using a three-dimensional petroleum system model calibrated to well data. A sensitivity analysis of source rock definition was performed in the case of the two main contributors, which are the Lower Jurassic Gordondale Member of the Fernie Group and the Upper Devonian–Lower Mississippian Exshaw Formation. This sensitivity analysis included variations of assigned total organic carbon and hydrogen index for both source intervals, and in the case of the Exshaw Formation, variations of thickness in areas beneath the Rocky Mountains were also considered. All of the modeled source rocks reached the early or main oil generation stages by 60 Ma, before the onset of the Laramide orogeny. Reconstructed oil accumulations were initially modest because of limited trapping efficiency. This was improved by defining lateral stratigraphic seals within the carrier system. An additional sealing effect by biodegraded oil may have hindered the migration of petroleum in the northern areas, but not to the east of Athabasca. In the latter case, the main trapping controls are dominantly stratigraphic and structural. Our model, based on available data, identifies the Gordondale source rock as the contributor of more than 54% of the oil in the Athabasca and Peace River accumulations, followed by minor amounts from Exshaw (15%) and other Devonian to Lower Jurassic source rocks. The proposed strong contribution of petroleum from the Exshaw Formation source rock to the Athabasca oil sands is only reproduced by assuming 25 m (82 ft) of mature Exshaw in the kitchen areas, with original total organic carbon of 9% or more.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Source rock contributions to the Lower Cretaceous heavy oil accumulations in Alberta: a basin modeling study
Series title:
American Association of Petroleum Geologists Bulletin
DOI:
10.1306/11141111064
Volume
96
Issue:
7
Year Published:
2012
Language:
English
Publisher:
American Association of Petroleum Geologists (AAPG)
Publisher location:
Tulsa, OK
Contributing office(s):
Central Energy Resources Science Center
Description:
24 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
American Association of Petroleum Geologists Bulletin
First page:
1211
Last page:
1234
Country:
Canada
State:
Alberta