Cynthia L. Riediger¹, Shona Ness¹, Martin Fowler², N. Taskin Akpulat¹

(1) University of Calgary, Calgary, AB
(2) Geological Survey of Canada, Calgary, AB

ABSTRACT: Timing of Oil Generation and Migration, northeastern British Columbia and southern Alberta. Signficance for Understanding the Development of the eastern Alberta Tar Sands Deposits

The origin and timing of emplacement of the enormous bitumen/heavy oil deposits in eastern Alberta have been studied and debated since the early work of Deroo and others in 1977. Based on biomarker characteristics, the main source rock for these deposits is the Devonian-Mississippian Exshaw Formation, although there may be minor contributions from other source rocks. The conventional view regarding the timing of oil migration, based on burial history modelling from southern Alberta, is that oils arrived at the eastern Alberta reservoirs over roughly the same time span (about 70 to 55 Ma), however, it was difficult to reconcile this migration scenario with observed patterns of biodegradation. In this study, burial history models were constructed for several wells in (a) Alberta/B.C. (Peace River Embayment (PRE) region), and (b) southern Alberta, using the Platte River BasinMod1D (r) program. In the PRE region, peak hydrocarbon generation occurred between about 110 and 80 Ma near the Alberta-B.C. border, but much earlier in the west (between 240-230 Ma close to the edge of the Foothills Belt), with little remaining oil potential by Jurassic time. The models thus suggest that significant hydrocarbon generation and migration was occurring prior to, during and after deposition of Lower Mannville reservoir strata (Aptian age) in eastern Alberta. In contrast, the Exshaw Formation in southern Alberta did not achieve peak hydrocarbon generation until about 60-55 Ma. These results have important implications for understanding the relative timing of hydrocarbon charging, and biodegradation of hydrocarbons, in the tar sands-heavy oil belt of eastern Alberta.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado