Tar sands

Oil sands, formerly referred to as tar sands, are sandy substrates that contain large deposits of bitumin, a kind of fossil fuel. Bitumen is a thick, viscous, black, sticky, tar-like form of liquid petroleum , but its physical consistency is comparable to that of cold molasses. Oil sands occurring at or near the surface can be mined using open-pit techniques. The bituminous materials are then extracted by heating and the hydrocarbons refined and manufactured into a synthetic petroleum product. Once the readily extractable, surface deposits are extracted, deeper bitumen may be mined using steam assisted, in situ techniques that decrease viscosity and allow the bitumen to flow so it can be pumped to the surface.

Mined oil sand typically contains 10-12% bitumen, 4-6% water, and 80-85% mineral sand and clays. About 2.2 tons (2 tonnes) of oil sand must be processed to produce one barrel (0.16 m³) of liquid petroleum. About 75% of the bitumen present can typically be recovered from mined oil sand. After processing, the sand waste and any unextracted bitumen are eventually used to back-fill and contour minedout areas, which are then seeded with vegetation to reclaim a stable plant cover.

Most economically recoverable oil sand occurs at or fairly near the ground surface. Initially it is mined in enormous open pits, using extremely large trucks and industrial shovels, among the biggest of their kind in the world. After the open-pit mining, remaining deposits deeper than about 250 feet (75 m) and up to 1,300 ft (400 m) or deeper are recovered using so-called in situ,or in-site practices. Various techniques are used for in situ extraction of bitumen and heavy crude oil. They include the injection of steam, solvents, or carbon dioxide to reduce the viscosity of the heavy fluids so they can flow and be collected and pumped to the surface. The largest in situ recovery plant in Alberta is located at Cold Lake, where steam injection is used to enhance the ability of the bitumen to flow. This allows it to be pumped to the surface, where it is treated with liquid natural-gas hydrocarbon condensate to reduce its viscosity. The treated bitumen is then shipped by pipeline to a specialized refinery complex where a relatively light synthetic petroleum is manufactured from the heavy, bituminous, crude fossil fuel.

The world's largest resources of oil sand occur in northern Alberta, Canada, and in Venezuela, in northern South America. In Alberta, there are about 54-thousand mi² (141-thousand km²) of oil-sand deposits. This region contains a total estimated resource of 1.6 trillion barrels (0.25 trillion m³)of bitumen, of which about 311 billion barrels (49 billion m³) are thought to be potentially recoverable using known mining and extraction technologies. Once processed, this bitumen could yield an estimated 189 billion barrels (30 billion m³) of synthetic petroleum.

The first pilot plant to process oil-sand bitumen was constructed in Alberta in 1962. The first full-scale facility was developed between 1964 and 1967, with an initial capacity of 31,000 barrels per day (4.9-thousand m³/day). During the 1990s, extremely large investments were made to mine and process the oil-sand deposits of Alberta. Between 1996 and 2000, the total investment in development of this resource was $11 billion (Can.), and it was $4.2 billion in 2000 alone. In the year 2000, 66,000 people were directly employed in the oil-sand industry, and the Government of Alberta received royalties of $711 billion. In 2001, oil sands were yielding about one-third of all the petroleum produced in Canada, and continued investment is expected to raise this to 50% by 2005. That would be equivalent to about 10% of the total production of petroleum in North America. Clearly, oil sands are a key component of the resource of liquid fossil fuels in North America, and a critical element contributing to the domestic energy security on the continent.

The mining and processing of oil sands results in important environmental impacts, although the most intense effects are restricted to the immediate vicinity of the industrial operations. For example, the development of mine sites, refineries, and pipelines results in severe direct damage to local natural habitats. In the case of open-pit mine development, the soil and other overburden removed from the site are generally stockpiled for use as a top-dressing during the reclamation of the pit after it is mined out. The original surface materials are conserved for this use because they provide a much more hospitable material for plant establishment and growth than does processed oil-sand waste, which is a highly mineral and infertile substrate. The reclamation usually attempts to re-create a facsimile of the original contours of the landscape, and is intended to establish a self-maintaining vegetation with at least as high a level of productivity as what occurred prior to the mining. The reclamation effort is typically designed to develop grassland, forest, or wetland habitats, or a mixture of these. Often, the intention is to establish vegetation dominated by native species of plants. The resulting habitats may then be attractive to indigenous species of birds, mammals, and other animals.

The process by which bitumen is extracted from oil sand and then manufactured into synthetic petroleum results in some emissions of sulfur dioxide , a toxic gas, into the atmosphere . The permissible amounts of emissions are regulated within levels intended to prevent local vegetation damage. This is achieved by the use of scrubbing technologies that remove most sulfur dioxide from the flue gases before they are vented to the ambient environment . The mining and processing processes also require extremely large inputs of energy to drive their processes. Industrial engineers have been working to make the processes run more efficiently, and they anticipate achieving a 45% reduction of carbon dioxide emissions per barrel by 2010, compared to 1990 levels. This will result in large savings in process costs, while also reducing the emissions of carbon dioxide, an important greenhouse gas, to the atmosphere.

[Bill Freedman Ph.D. ]

RESOURCES

BOOKS

Fitzgerald, J. Gold with Grit: The Alberta Oil Sands. Sidney, BC: Gray's Publishing, 1978.

Lyttle, R. B. Shale Oil and Tar Sands: The Promises and Pitfalls. Danbury, CT: Impact Books, 1982.

Perrini, E. M. Oil from Shale and Tar Sands. Park Ridge, NJ: Noyes Data Corporation, 1975.

OTHER

Government of Alberta. Oil Sands. 2002 [cited July 2002]. <http://www.energy.gov.ab.ca/com/Sands/default.htm>.

tar sand Oil reservoir where the volatiles have escaped and the rock has become impregnated with hydrocarbon residue. Sometimes this occurs in commercial quantities, as at Athabasca, Alberta, Canada; the sands are mined open-cast and treated with steam and hot water to release the oil.