| Clearwater Formation | |
|---|---|
| Stratigraphic range:Albian | |
| Type | Geological formation |
| Unit of | Mannville Group |
| Sub-units | Wabiskaw Member |
| Underlies | Grand Rapids Formation |
| Overlies | McMurray Formation |
| Thickness | up to 85 metres (280 ft)[1] |
| Lithology | |
| Primary | Shale |
| Other | Sandstone,siltstone |
| Location | |
| Coordinates | 58°00′49″N111°20′38″W / 58.01365°N 111.34377°W /58.01365; -111.34377 (Clearwater Formation) |
| Region | northeastern and central Alberta |
| Country |  Canada |
| Type section | |
| Named for | Clearwater River |
| Named by | R.G. McConnell, 1893 |
TheClearwater Formation is astratigraphic unit ofEarly Cretaceous (Albian)age in theWestern Canada Sedimentary Basin in northeasternAlberta, Canada.[2] It was first defined by R.G. McConnell in 1893 and takes its name from theClearwater River nearFort McMurray.[3]
Impermeable marineshales in the Clearwater Formation provided part of thetrapping mechanism for the underlyingAthabasca oil sands in theMcMurray Formation.Sandstone units in the Clearwater Formation, including the Wabiskaw Member, can containoilsand andheavy oil resources.[1]
Nearly complete specimens ofplesiosaurs andichthyosaurs, as well as oneankylosaur, have been recovered from the formation during oilsand mining.[4]
The Clearwater Formation consists of primarily of black and green shale, with some interbedded grey and green sandstone and siltstone, andironstoneconcretions. To the southeast ofCold Lake it includes massive hydrocarbon-bearing,glauconitic salt-and-pepper sandstones with interbedded shales.[1]
The Wabiskaw Member forms the base of the Clearwater Formation. It consists of glauconitic sandstones with interbeds of black fissile shale, and it includes oilsand and heavy oil in some areas.[1] It was defined in wellBarnsdall West Wabiskaw No. 1 (located betweenWabasca River andLesser Slave Lake incentral Alberta) by P.C. Badgley in 1952.[5]
The Clearwater Formation is present in the subsurface of northeastern and central Alberta, and is exposed on lower course of theAthabasca River, as well as along theChristina River, a tributary of theClearwater River southeast ofFort McMurray. It reaches a maximum thickness of 85 metres (280 ft) on the Athabasca River, thins out to 6 metres (20 ft) in theCold Lake area, and wedges out towards the south. It is not present south ofEdmonton.[1]
The Clearwater Formation is part of theMannville Group. It is conformably overlain by theGrand Rapids Formation and conformably overlies theMcMurray Formation. It is equivalent to theBluesky Formation and the lowerSpirit River Formation in thePeace River region, and may be equivalent to theCummings Member in theLloydminster region.[1]
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The Clearwater Formation was deposited in marine, near-shore and estuarine environments on the eastern side of theWestern Interior Seaway, and it contains marine and, rarely, terrestrial fossils. Workers at mines near Fort McMurray have made a number of significant finds while removing Clearwater strata to expose underlying oilsand deposits.Plesiosaurs such asNichollssaura andichthyosaurs such asAthabascasaurus, some of them nearly complete, have been recovered atSyncrude Canada Ltd.'s mines.[4][6]
The well-preserved holotype specimen of the nodosauridBorealopelta markmitchelli has also been recovered at theSuncor Millennium Mine. Plesiosaurs and ichthyosaurs were large marine reptiles, but the ankylosaur was an armoured dinosaur and represents a terrestrial animal that became entombed in the sea floor approximately 200 kilometres (120 mi) from the nearest known paleo-shoreline. Its bloated carcass probably washed out to sea and floated for several days before sinking to the sea floor.[4]
All of the specimens now reside at theRoyal Tyrrell Museum of Palaeontology.[4]
The formation contains oilsand in theCold Lake andPrimrose Lake region.Heavy oil is produced from the loose sandstones of the Wabiskaw Member by means ofhorizontal drilling in theWabasca oil field, and the Wabiskaw containssurface-mineable oilsand in the Fort McMurray area.
The oilsands of the Clearwater Formation are more difficult to tap than those of the McMurray Formation.Cenovus Inc.'s Tucker thermal oilsands project which opened in 2006 began to post a modest return in 2013.[7]Cenovus Inc. (CVE), with its head office in Calgary, Alberta, Canada is an integrated oil and natural gas producer.
Canadian Natural Resources use "employs cyclic steam or "huff and puff" technology to develop bitumen resources. This technology requires one well bore and the production consists of the injection and production phases. First steam is "injected for several weeks, mobilizing cold bitumen". Then the flow "on the injection well is reversed producing oil through the same injection well bore. The injection and production phases together comprise one cycle. "Steam is re-injected to begin a new cycle when oil production rates fall below a critical threshold due to the cooling of the reservoir."[8]
"Roughly 35 per cent of allin situ production in the Albertaoil sands uses a technique called High Pressure Cyclic Steam Stimulation (HPCSS), which cycles between two phases: first, steam is injected into an underground oilsands deposit to soften the bitumen; then, the resulting hot mixture of bitumen and steam (called a "bitumen emulsion") is pumped up to the surface. The process is then repeated multiple times."[9] AnAlberta Energy Regulator (AER) news release explained the difference between high pressure cyclic steam stimulation (HPCSS) and steam assisted gravity drainage (SAGD). "HPCSS has been used in oil recovery in Alberta for more than 30 years. The method involves injecting high-pressure steam into a reservoir over a prolonged period of time. As heat softens the bitumen and water dilutes and separates the bitumen from the sand, the pressure creates cracks and openings through which the bitumen can flow back into the steam-injector wells. HPCSS differs from steam assisted gravity drainage (SAGD) operations where steam is injected at lower pressures without fracturing the reservoir and uses gravity drainage as the primary recovery mechanism."[10]Canadian Natural Resources Limited's (CNRL) Primrose and Wolf Lake in situ oil sands project nearCold Lake, Alberta in the Clearwater Formation, operated by CNRL subsidiaryHorizon Oil Sands, use the high pressure cyclic steam stimulation (HPCSS).(AER 2013)
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