Regional geology and sedimentology of the basal Cretaceous Peace River OilSands deposit, north-central Alberta

Major oil sand deposits, including Athabasca, Cold Lake and Peace River, ar e found in Lower Cretaceous strata of northern Alberta. The Peace River dep osit comprises bitumen-rich sands from the Aptian-Albian Gething Formation, Ostracode Zone, and Bluesky Formation, which overlay Paleozoic and older M esozoic strata. Stratigraphic and sedimentologic data indicates these sedim ents were deposited as the Boreal Sea inundated the area from the north. The overall depositional framework shows a transgressive evolution from a f luvial/non-marine system (Gething Formation), to a brackish bay system (Ost racode Zone), and finally into a marginal marine estuarine complex (Bluesky Formation). Exploitable bitumen reserves at Peace River are contained pred ominantly within the 15 - 20 m thick estuarine sands of the Bluesky Formati on. 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-convent ional 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 accumula ted in a large stratigraphic trap, sealed by overlying Wilrich Member shale s of the Spirit River Formation. Mississippian carbonates, although saturat ed with bitumen locally, in effect provided the bottom seal to the reservoi r 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 r eservoir distribution and subsequently the location of prospective developm ent areas.