Oil shale is a fine-grained sedimentary rock containing significant amounts of kerogen (a solid mixture of organic chemical compounds), from which liquid hydrocarbons can be extracted. The name oil shale has been described as a promotional misnomer, since the rock is not necessarily a shale and its kerogen is not crude oil; it requires more processing than crude oil, which affects its economic viability as a crude oil substitute.[1][2] Deposits of oil shale are located around the world, including major deposits in the United States. Global deposits are estimated as equivalent to 2.8 trillion to 3.3 trillion barrels (450×109 to 520×109 m3) of recoverable oil.[2][3][4][5]
The chemical process of pyrolysis can convert the kerogen in oil shale into synthetic crude oil. When oil shale is heated to a sufficiently high temperature a vapor is driven off which can be distilled (retorted) to yield a petroleum-like shale oil?a form of non-conventional oil?and combustible shale gas (shale gas can also refer to gas occurring naturally in shales). Oil shale can also be burned directly as a low-grade fuel for power generation and heating purposes and can be used as a raw material in the chemical and construction materials industries.[6][2]
Oil shale has gained attention as an energy resource as the price of conventional sources of petroleum has risen and as a way for some areas to secure independence from external suppliers of energy.[7][8] At the same time, oil shale mining and processing involve a number of environmental issues, such as land use, waste disposal, water use and waste water management, and air pollution.[9][10] The oil shale industry is well-established in Estonia, China and Brazil, and to some extent in Germany, Israel and Russia.
Reserves
Main article: Oil shale reserves
Fossils in Ordovician oil shale (kukersite), northern Estonia
Fossils in Ordovician oil shale (kukersite), northern Estonia
Some analysts, along with the United States Geological Survey, draw a distinction between oil-shale resources and oil-shale reserves. "Resources" may refer to all oil shale deposits, while "reserves" is more narrowly defined as those deposits from which oil can profitably be extracted using existing technologies. Since extraction technologies are still developing, the amount of recoverable kerogen can only be estimated.[6][18] Although oil shale resources occur in many countries, only 33 countries possess deposits of possible economic value.[19][20] Well-explored deposits, which could be classified as reserves, include the Green River deposits in the western United States, the Tertiary deposits in Queensland, Australia, deposits in Sweden and Estonia, the El-Lajjun deposit in Jordan, and deposits in France, Germany, Brazil, China, and Russia. It is expected that these deposits would yield at least 40 liters of shale oil per tonne of shale, using the Fischer assay.[6][14]
A 2005 estimate set the total world resources of oil shale at 411 gigatons ? enough to yield 2.8 to 3.3 trillion barrels (520 km³) of shale oil.[2][3][4][5] This is more than world's proven conventional oil reserves, estimated to be 1.317 trillion barrels (209.4×109 m3), as of 1 January 2007.[21] The largest deposits in the world are found in the United States in the Green River basin, which covers portions of Colorado, Utah, and Wyoming; about 70% of this resource is located on federally owned or managed land.[22] Deposits in the United States constitute 62% of world resources; together, the United States, Russia and Brazil account for 86% of the world's resources in terms of shale oil content.[19] These figures are considered tentative, as several deposits have not yet been explored or analyzed.[6][2]
Industry
Main article: Oil shale industry
As of 2008 industry uses oil shale in Brazil, China, Estonia and to some extent in Germany, Israel, and Russia. Several additional countries were assessing their reserves or had built experimental production plants, while others had phased out their oil shale industry.[2] Oil shale is used for oil production in Estonia, Brazil, and China; for power generation in Estonia, China, Israel, and Germany; for cement production in Estonia, Germany, and China; and by chemical industries in China, Estonia, and Russia.[28][2][34][35] As of 2005, Estonia alone accounted for about 70% of the world's oil shale production.[34][36]
Romania and Russia have in the past run power plants fired by oil shale, but have shut them down or switched to other fuel sources such as natural gas. Jordan and Egypt are planning to construct oil shale-fired power plants, while Canada and Turkey plan to burn oil shale along with coal for power generation.[2][19][37] Oil shale is used as the main fuel for power generation only in Estonia, where the oil shale-fired Narva Power Plants accounted for 95% of electrical generation in 2005.[38]
Applications and products
Oil shale can be used as a fuel for thermal power plants, burning it (like coal) to drive steam turbines; some of these plants employ the resulting heat for district heating of homes and businesses. Sizable oil shale-fired power plants are located in Estonia, which has an installed capacity of 2,967 megawatts (MW), Israel (12.5 MW), China (12 MW), and Germany (9.9 MW).[19][46]
In addition to its use as a fuel, oil shale may also serve in the production of specialty carbon fibers, adsorbent carbons, carbon black, phenols, resins, glues, tanning agents, mastic, road bitumen, cement, bricks, construction and decorative blocks, soil additives, fertilizers, rock wool insulation, glass, and pharmaceutical products.[34] However, oil-shale use for production of these items remains small or only in its experimental stages.[6][2] Some oil shales yield sulfur, ammonia, alumina, soda ash, uranium, and nahcolite as shale oil extraction byproducts. Between 1946 and 1952, a marine type of Dictyonema shale was used for uranium production in Sillamäe, Estonia, and between 1950 and 1989 alum shale was used in Sweden for the same purposes.[6] Another of its uses has been as a substitute for natural gas, but as of 2008, producing shale gas as a natural gas substitute is not economically feasible.[47][48]
The oil derived from oil shale does not directly substitute for crude oil in all applications. It contains higher concentrations of olefins, oxygen, and nitrogen than conventional crude oil, as well as higher viscosities. By comparison with West Texas Intermediate, the benchmark standard for crude oil in the futures contract market, shale oil sulfur content ranges up to 9.5% by weight, where West Texas Intermediate's sulfur content is limited to no more than 0.42%.[49][50] The higher concentrations of these materials means that the oil must undergo considerable upgrading before being used as oil refinery feedstock.[51] Shale oil does not contain the full range of hydrocarbons used in modern gasoline production, and could only be used to produce middle-distillates such as kerosene, jet fuel, and diesel fuel.[4] Worldwide demand for these middle distillates, however, is increasing rapidly.[52]
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