Athabasca deposit

The Athabasca deposit, along with the neighboring Wabasca, Peace River, and Cold Lake heavy oil deposits, have together been estimated to contain 1.86 X 10 m (>1.17 X 10 bbl) of bitumen. The Vene2uelan deposits may at least contain >1.60 X 10 m (1.0 X 10 bbl) bitumen (2). Deposits of tar sand, each containing >3 x 10 m (20 x 10 bbl) of bitumen, have also been located in the United States, Albania, Italy, Madagascar,... 

The Athabasca deposits have been known since the early 1800s. The first scientific iaterest ia tar sands was taken by the Canadian government ia 1890, and ia 1897—1898, the sands were first drilled at PeHcan Rapids on the Athabasca River. Up until 1960, many small-scale commercial enterprises were attempted but not sustained. Between 1957 and 1967, three extensive pilot-plant operations were conducted ia the Athabasca region, each leading to a proposal for a commercial venture, eg, Suncor and Syncmde. 

The bitumen in the Athabasca deposit, which has a gravity on the API scale of 8°, is heavier than water and very viscous. Tar sand is a dense, soHd material, but it can be readily dug in the summer months during the winter months when the temperatures plunge to —45° C, tar sand assumes the consistency of concrete. To maintain acceptable digging rates in winter, mining must proceed faster than the rate of frost penetration if not, supplemental measures such as blasting are required. 

It is estimated that the total oil sands and carbonates may contain in the order of two and a half trillion barrels of in-place oil. Not all of this is recoverable. Less than 57. of the Athabasca deposit is recoverable by the mining methods using today s technology and perhaps less than 307. of the remaining oil in all the oil sands deposits is recoverable by in-situ techniques. This means however, that a total of about 300 billion barrels is potentially recoverable. This compares very favourably with the 8 billion barrels estimated in our Canadian conventional oil reserves. In years of supply it equates to 400 to 500 years of reserves - a very attractive prize. 

Reserves of tar sands or oil sands are found in Venezuela, the Uinta Basin of Utah, and extensively in the Athabasca deposits in Alberta, Canada. In the late 1940s, Sidney Ellis and Karl Clark developed processes to enable valuable oil to be... 

The oil sands from the Athabasca deposits are a mixture of sand grains, water, and high-viscosity crude hydrocarbon called bitumen. At room temperature, bitumen is a semisolid, but will convert to a viscous liquid at about 300°F (149°C). Sand grains are about 0.075 to 0.25 mm in diameter with small amounts of attached clay. The grains are all in direct contact and wet with a thin continuous sheetlike layer of water. Bitumen fills the void between the wetted sand grains and forms a continuous phase through the pores. Bitumen is about 17% to 18% of the mass. The composition of Athabasca oil sand bitumen is provided in TABLE 12-6. 

These major deposits are estimated to contain 158 Gm3 (967 GBBL) of bitumen. The Athabasca deposit is the world s largest deposit covering an area roughly the size of Belgium and contains 118... 

Of these deposits, the Athabasca deposit has received the most attention from scientists and commercial developers since it is the largest and fortunately also has the shallowest overburden thus permitting surface mining. Again, because of the shallow overburden, the Athabasca oil sands deposit is the only deposit in the world to have attracted large-scale commercial development. Smaller developments have taken place in Venezuela, Trinidad, Albania, Rumania and in the U.S.S.R. 

The Athabasca deposit is the site of two operational facilities Suncor, Inc. with a daily production of 8600 m3 of synthetic crude and Syncrude Canada Limited with a design production of... 

The geological stratification of the Athabasca deposit is presented in Figure 2. As with most rivers in this region of Western Canada, the Athabasca River has gouged a deep river valley, exposing the oil sands deposits along its banks. On warm days the bitumen oozes from the river banks and eventually works its way to the water line. Native Indians used this bitumen, mixed with spruce gum, to patch their canoes. 

The Athabasca deposit is relatively rich with bitumen saturation up to 18% by weight. 

Fig. 2. Genera] view of upgrading plant for processing bitumen mined from Athabasca deposit. In the foreground is the sulfur stockpile in the background is a tailings pond. Right background shows the extraction plant left is the coke pile. (Alberta Government Photographic Service)...

The tar sands situated in Alberta consist of oil-bearing sandstones. Surface exposures occur in parts of the Athabasca deposit, but much of the deposit lies 100 m or more beneath the surface. Oil present in these Lower Cretaceous sandstone deposits is very viscous, thick, and partially oxidized so that it cannot be recovered by pumping alone. Hence, the term tar or bitumen describes this heavy oil fraction, which averages about 12% ranging up to as much as 18% of the deposit by weight. Deposits with less than 2-3% bitumen are excluded from the reserve data given in Table 17.4. 

The surface exposures and the near surface deposits (<45 m of cover) of the Athabasca region can be strip-mined for bitumen recovery. They amount to about 10% of the Athabasca deposit. The remainder of the Alberta tar sands lie under 75 m or more of overburden. It is uneconomical to surface mine, and too poorly consolidated for underground mining. These deeper deposits are yielding bitumen to the surface via various in situ techniques. 

In the more localized context of the Athabasca deposit, inconsistencies arise presumably because of the lack of mobility of the bitumen at formation temperature (approximately 4°C, 39°F). For example, the proportion of bitumen in the tar sand increases with depth within the formation. Furthermore, the proportion of the nonvolatile asphaltenes or the nonvolatile asphaltic fraction (asphaltenes plus resins) in the bitumen also increases with depth within the formation that leads to reduced yields of distillate from the bitumen obtained from deeper parts of the formation. In keeping with the concept of higher proportions of asphaltic fraction (asphaltenes plus resins), variations (horizontal and vertical) in bitumen properties have been noted previously, as have variations in sulfur content, nitrogen content, and metals content. Obviously, the richer tar sand deposits occur toward the base of the formation, but the bitumen is generally of poorer quality. 

The available evidence is specific to the Athabasca deposit. For example, bitumen obtained from the northern locales of the Athabasca deposit (Bitumount, Mildred-Ruth Lakes) has a lower amount (by weight values approximately 16-20%) of the nonvolatile asphaltene fraction than the bitumen obtained from southern deposits (Abasand, Hangingstone River approximately 22-23 /o by weight asphaltenes). In addition, other data indicate that there is also a marked variation of asphaltene content in the tar sand bitumen with depth in the particular deposit. 

Of the Canadian deposits, the largest, Athabasca, is at least 4 times the size of the largest conventional oil field, Ghawar, in Saudi Arabia (5). Of the Athabasca s estimated 600 billion barrels of bitumen, about 60 billion barrels could be recovered by surface mining of the oil sand followed by beneficiation to separate the oil. Currently two commercial plants are producing synthetic crude oil from the Athabasca deposit. In these operations, the oil sands are first mined, and the bitumen is extracted by a hot-water flotation process, which produces a bituminous froth. After breaking the froth, the separated bitumen is subsequently upgraded by refineiy-type processes to produce synthetic crude oil. In order to understand the nature of the froths produced, the nature of oil-sand structure will be reviewed first, and then the flotation process from which froths are produced will be examined. 

In the shallow regions of the Athabasca deposit, the oil is in a drainage basin that was filled in with sediments as it was alternately flooded by a sea (estuarial environment) and then rivers (fluvial environment), so that a number of distinct depositional environments of estuarine and marine sediment occurred (10—15). As a result, the oil-bearing sands have great variability in their compositions and properties. 

Athabasca deposit, the temperature dependence of the viscosity is shown in Figure 6. The Athabasca bitumen rheology is not typical of that in other world locations. For example, the rheology of bitumen in the Utah deposits, which have much higher effective viscosities (48, 49), is more complex and exhibits markedly non-Newtonian behavior (47). 

Two countries, Canada and Venezuela, hold over 40% each of the total extraheavy hydrocarbon reserves. Alberta tar-sands fields in western Canada, particularly the mammoth Athabasca deposit, contain over 250 billions tons of bitumen which has to be produced by surface mining because it is not fluid under reservoir conditions, owing to the cold climate and the low depth (100—150m). Because of relatively adverse conditions, only 40 billion tons can be recovered by current technology. The Orinoco Oil Belt in eastern Venezuela contains a staggering 200 billion tons of extraheavy crude oils, from which 40 billion ton reserves can be tapped by widespread oilfield teehniques. Other reserves are found in countries of the former USSR, USA, and China. These figures are to be eompared with Saudia Arabia s 36 billion tons of eonventional erude oil reserves and South Afriea s eoal reserves whieh are equivalent to 37 billion tons of petroleum. 

The processing of extraheavy crude oils/bitumens is extremely important because world reserves amount to 450 billion tons. To date, the mammoth Athabasca deposit in Alberta, Canada, and the Orinoco Oil Belt in western Venezuela are the largest. Together, Canada and... 

Accounts of early exploration and examination of the Athabasca deposit can be found elsewhere [3, 11-13] as can accounts of some of the early process development efforts [14-16], Commercial plants now mine oil sands and then extract bitumen using the hot water conditioning and flotation process (at production levels of over 300,000 bbl/d). The extracted bitumen is subsequently upgraded by refinery type processes to produce light, sweet crude oil. 

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