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Cold Lake Oil Sands

The Cold Lake oil sands are a group of bitumen containing formations in the Cold Lake region of Alberta, Canada. The amount of hydrocarbons is disputed for the Cold Lakes Oil Sands, but likely contains between 75 and 164 billion barrels of original oil in place (OOIP), with the Energy Resources Conservation Board listing the volume as approximately 220 billion barrels.

The Cold Lake area contains oil in several stacked deposits in what is known as the Mannville group. These are designated the 'A', 'B', 'C' and 'D' units in literature. The Mannville averages 700 feet of total thickness in the Cold Lake area. Oil saturation is dependent on the amount of clay matrix, the number of shale interbeds and the position of the reservoir sands in relation to the oil/water contact. Sands on the east and west flanks are water saturated. Sands with more than 10% 'mud matrix' are usually water-saturated in this area.

Depositional History


The Cold Lake deposits are located in the Western Canada Basin, which is an asymmetrical, synclinal foreland basin. The Foreland basin itself began development in the mid-Jurassic due to an uplift in the west. The Mississippian to Jurassic aged deposits eroded away in the Cold Lake region, leaving the eroded Late Devonian sand as the surface the Cretaceous and later sands were deposited on. .

The Mannville group was deposited on the eroded Late Devonian Frasnian sands, creating an unconformity. The Lower Mannville is due to erosion after a late Jurassic uplift in Western Canada. This uplift was continued in the early Cretaceous due to the Nelson and Cassiar-Omineca batholiths. The deposited sediment initially came mostly from the Canadian Shield. This led to the deposition of the 'D' unit. After this sand was deposited the Artic Sea transgressed to the southeast. It was during this time that the 'C' unit was deposited. During this time the Canadian shield was still the main source of sediments, but a western orogeny contributed to the sediments as well. After the 'C' unit was deposited the Arctic sea regressed north. Then the 'B' unit was deposited. It was during this time that the main source of sediments changed from the Canadian Shield in the east, to the orogeny to the west. Lastly was a transgressive period that coincided with the deposition of the 'A' unit. It should be noted that there was not much compaction after the deposition of the Mannville group.

Lower Mannville
The Lower Mannville Cold Lake Oil Sands formations were mainly deposited as a large delta complex as the Artic Sea advanced into northern Alberta during subsidence.

McMurray Formation
The lowest sand is what is referred to as the 'D' sand in most writing. It is actually the McMurray Formation. The thickness of the McMurray Formation in the Cold Lake deposits varies from 250 feet in the northwest to 20 feet to the southeast. The bitumen saturation is greatest in these thinner high areas. The basal sands in McMurray were deposited as fluvial sheet sands on the eroded Beaverhill Lake. Eventually this led to the McMurray Formation sands being laid down in a tidal-flat beach environment. There is no oil the in lower 'D' sands, but the upper unit forms good oil deposits. This sand contains an estimated 7% of the hydrocarbons.

Upper Mannville
The sandstones in the upper Mannville are stacked fluvial deposits, stacked crevasse splays and amalgamated channel and marine shoreline facies. It is predominantly continental in the west, and marginally marine in the eastern part. (Cold Lake is more eastern). This means that the facies are consistent with a fluvially dominated delta.

Clearwater Formation
Above the McMurray Formation sand is what is referred to in writing as the 'C' sand. This sand is actually the Clearwater Formation. The Clearwater formation unit shows at least two distinct depositional cycles of deltaic sedimentation. The Clearwater formation was deposited in an incised valley system. These valleys were formed during regression as river systems advanced northwards. This is shown as a series of bar sands with inter-bar sands/ silts and shale. Coarse grain sizes are indicative of high-energy one directional currents. Additionally there is not much diversity or density of Planolites and Skolithos. These observations are evidence for a fluvial depositional environment. There is also abundant carbonaceous detritus, suggesting that terrestrial plants were within the vicinity at the time of deposition. Heterolithic sandstones point to undulations between suspended load and bedload depositions. This would suggest twice daily tidal changes in tidal flats. Like the McMurray formation, the bitumen is primarily located in the thinner, higher areas. The Clearwater Formation is mostly near shore marine sandstones and is 300-450 feet below the top of the Mannville. This sand contains an estimated 20% of the hydrocarbons.

Grand Rapids Formation
The Grand Rapids formation is mainly non-marine feldspar, and salt sandstones, with siltstones and shale with thin coal beds.

Lower Grand Rapids Formation
Above the Clearwater formation is what is referred to in writing as the 'B' unit contains both beach and deltaic sands.

The sand is actually the Lower Grand Rapids Formation. This sand contains an estimated 48% of the hydrocarbons.

Upper Grand Rapids Formation
Above the Lower Grand Rapids formation is what has been labeled as the 'A' unit. This is actually the Upper Grand Rapids Formation. Sands of the Upper Grand Rapids Formation were deposited in a fluvial flood plain, and are discontinuous silts and shale. The 'A' unit also contains gas. This sand contains an estimated 25% of the hydrocarbons.



East-West Cross Section of Cold Lake Deposits. Modified from Jardine 1974 and Minken 1974

Seal
The Mannville group is capped on top by the Joli Fou Formation of the Colorado Group shale. This layer of mostly marine shale with small amounts of sand creates a seal on top of the Mannville group.

Trapping Mechanism
The reservoirs themselves form a gently folded anticline that plunges towards the south.

Formation Characteristics
Porosity is from 28-43 percent and averages 37 percent. The clean oil sands average between 300 and 1300 millidarcies but can be up to 3000 millidarcies.

The depth below the surface ranges from 1000 to 2000 feet. It covers and area of approximately 3160 metric acres. It has an average of 42 feet of pay thickness.

The net thickness of the oil sands is up to as much as 200 feet in certain areas.

Hydrocarbon Characteristics
The hydrocarbons in the Cold Lake area are thermally immature and mainly bitumen.

The bitumen is between 4000 and 100000 centipoise.

The oil is approximately 10-12 degrees API, with the lightest oil being 14.5 degrees API.

The Sulfur content is between 3 and 4 percent by weight.

Hydrocarbon Origin
As previously discussed the Mississippian to Jurassic aged rocks below the Cold Lake area eroded away. This would make the Devonian rocks below appear to be the best option for a source rock. Until the geochemistry of the oil was studied in greater detail, it was believed that the Devonian sands were the source rock, however further research showed that oil from Devonian source rocks lacked the high Sulfur content seen in the Cold Lake area. This research also showed that the Mississippian and early Jurassic sands to the west of Cold Lake produced oil that had the correct Sulfur content. Pentadecane and longer alkane chain data also points to the source rocks for the Western Canada Basin, Cold Lake in particular, as being very similar to the Bakken Formation in the northern United States. Total organic carbon for Mississippian cores just to the west of Cold Lake, and therefore the most likely source rock, is between 14% and 18%. The Kerogen type is almost exclusively amorphous kerogen with liptinite.

One hypothesis is that the oil was, due to organic acid salts, much more soluble in the water. This would mean that the hydrocarbons were transported in the compaction waters and were 'precipitated out' when this water reaches a formation with different physical-chemical conditions.

Field Development
The Cold Lake region currently contains more than 150 well pads, each having 20-30 wells. Cyclic Steam Injection is the main mechanism used to recover oil from the deposits. It involved injecting steam for several months and then leaving the steam for another several months to soak. The steam injection is scheduled so that the steam zones migrate across the field. Satellite mapping of changes in topology is also used to help verify the location of the injected steam underground, as well as where the bitumen is being drained from.