'Lakes of Heavy Oil': Cretaceous Incised Valley Fill Reservoirs of the Cold Lake Giant Oilfield, Alberta, Canada
Clive R. Jones1, Howard R. Feldman2, Kevin L. Treptau1, G. Glen McCrimmon1, and Bogdan L. Varban1
1Imperial Oil Resources, Canada
2ExxonMobil Exploration Company, USA
The Cold Lake heavy oil field, Alberta, Canada contains in-place bitumen resources estimated at 21 billion barrels. The primary reservoirs occur within large incised valley fills of the Albian (Cretaceous) Clearwater Formation. To date over 800 Million barrels of 10° API bitumen have been produced, with recent rates surpassing 150,000 barrels per day from over 4,500 producing wells. Bitumen is recovered via in situ cyclic steam stimulation (CSS) which has traditionally required closely-spaced wells (4-8 acre). As a result, there is a rich collection of well log and core data. This presents a unique opportunity to investigate, in detail, the transition from fluvial and tide-dominated incised valley deposits through to open marine depositional environments using over 1000 wells and 400 cores over an area of 3,200 km2. Detailed facies description and identification of sequence boundaries in core, tied to prominent well log markers in the densely-spaced well dataset, allows unambiguous correlation of valley fill successions throughout the area.
The Clearwater Formation consists of at least 10 discrete incised valley fills with depths of incision ranging from 30 to 120 m. Each incised valley fill shows an updip to downdip trend from sandstone-dominated fluvial or upper estuarine facies to mudstone-prone estuarine or marine facies. These valley systems are nested within a broad incised valley belt, located predominantly on the Imperial Oil leases, and display a progressively basinward-stepping stratigraphic architecture. The entire Clearwater system is capped by a regional marine flooding surface that is correlative throughout the area. When preserved, the incised valleys terminate downdip as thin (< 2 m) sheets of marine sandy mudstone. Of significance, none of the valleys appear to correlate with time-equivalent downdip lowstand deltas or sandy shoreline deposits. The presence of deep incised valley successions by themselves cannot therefore be used in isolation to predict sand delivery to a lowstand shoreline or to more basinal areas.
AAPG Search and Discovery Article #90075©2008 AAPG Hedberg Conference, Banff, Alberta, Canada