Abstract

Major oil sand deposits, including Athabasca, Cold Lake and Peace River, are found in Lower Cretaceous strata of northern Alberta. The Peace River deposit comprises bitumen-rich sands from the Aptian-Albian Gething Formation, Ostracode Zone, and Bluesky Formation, which overlay Paleozoic and older Mesozoic strata. Stratigraphic and sedimentologic data indicates these sediments were deposited as the Boreal Sea inundated the area from the north. The overall depositional framework shows a transgressive evolution from a fluvial/non-marine system (Gething Formation), to a brackish bay system (Ostracode Zone), and finally into a marginal marine estuarine complex (Bluesky Formation). Exploitable bitumen reserves at Peace River are contained predominantly within the 15-20 m thick estuarine sands of the Bluesky Formation. Where combined with underlying fluviatile sands of the Ostracode Zone, net pay can reach up to 30 m in thickness. These sands are penetrated at an average depth of 550 m and production of the bitumen relies on non-conventional recovery methods. Heavy oil (<10 API) reserves in-place are estimated at almost 90 billion barrels. Original oil migration into Lower Cretaceous strata at Peace River accumulated in a large stratigraphic trap, sealed by overlying Wilrich Member shales of the Spirit River Formation. Mississippian carbonates, although saturated with bitumen locally, in effect provided the bottom seal to the reservoir over much of the area. The Peace River oil sand deposit lies in direct proximity to the structural axis of the Peace River Arch. Lower Cretaceous sedimentation was strongly influenced by reactivation of underlying faults associated with flexure and compression of this feature. Post-Bluesky faulting is observed to effect reservoir distribution and subsequently the location of prospective development areas.

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