n.
A black or dark brown shale containing hydrocarbons that yield petroleum by distillation.
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A black or dark brown shale containing hydrocarbons that yield petroleum by distillation.
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A sedimentary rock containing solid, combustible organic matter in a mineral matrix. The organic matter, often called kerogen, is largely insoluble in petroleum solvents, but decomposes to yield oil when heated. Although “oil shale” is used as a lithologic term, it is actually an economic term referring to the rock's ability to yield oil; oil shale appears to be the cheapest source after natural petroleum for large amounts of liquid fuels. No real minimum oil yield or content of organic matter can be established to distinguish oil shale from sedimentary rocks. Additional names given to oil shales include black shale, bituminous shale, carbonaceous shale, coaly shale, cannel shale, cannel coal, lignitic shale, torbanite, tasmanite, gas shale, organic shale, kerosine shale, coorongite, maharahu, kukersite, kerogen shale, algal shale, and “the rock that burns.” See also Kerogen.
The world's oil shale deposits represent a tremendous store of fossil energy. It has been estimated that the organic matter in sedimentary rocks contains 1.2 × 1016 tons (1.1 × 1016 metric tons) of organic carbon, nearly 1000 times that found in coals. Although part of that organic carbon has matured to produce oil and gas, most of it is still oil shale. Unfortunately, most of this tremendous resource is not well known. Oil shales occur on every continent in sediments ranging in age from Cambrian to Tertiary. Estimates for the total oil resource in shales of all grades reached 1.75 × 1015 barrels. Just 1% of that total shale oil represents more oil than the world is expected to produce as natural petroleum (2 × 1012 bbl). Oil shale represents a tremendous supply of liquid fuels.
Although the oil potential of the world's oil shales is great, commercial production of this oil has been considered uneconomic. Oil shales are lean ores, producing only limited amounts of oil which historically has been low in price. Mining and heating 1 ton of relatively rich oil shale yielding 25 gal/ton produces only 0.6 bbl of oil.
Shale oil is produced from the organic matter in oil shale when the rock is heated in the absence of oxygen (destructive distillation). This heating process is called retorting, and the equipment that is used to do the heating is known as a retort. The rate at which the oil is produced depends upon the temperature at which the shale is retorted. Most references report retorting temperatures as being about 500°C (930°F).
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| Wikipedia: Oil shale |
| Oil shale | |
|---|---|
| — Sedimentary Rock — | |
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| Combustion of oil shale | |
| Composition | |
| Primary | Kerogen, Quartz, Feldspar, Clay, Carbonate, Pyrite |
| Secondary | Uranium, Iron, Vanadium, Nickel, Molybdenum |
Oil shale, an organic-rich fine-grained sedimentary rock, contains significant amounts of kerogen (a solid mixture of organic chemical compounds) from which technology can extract liquid hydrocarbons. The name oil shale represents a double misnomer, as geologists would not necessarily classify the rock as a shale, and its kerogen differs from crude oil. Kerogen requires more processing to use than crude oil, which increases its cost as a crude-oil substitute both financially and in terms of its environmental impact.[1][2] Deposits of oil shale occur around the world, including major deposits in the United States of America. Estimates of global deposits range from 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. Heating oil shale to a sufficiently high temperature will drive off a vapor which processing can distill (retort) to yield a petroleum-like shale oil—a form of unconventional oil—and combustible oil-shale gas (the term shale gas can also refer to gas occurring naturally in shales). Industry can also burn oil shale directly as a low-grade fuel for power generation and heating purposes and can use it as a raw material in chemical and construction-materials processing.[2][6]
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 raise a number of environmental concerns, such as land use, waste disposal, water use, waste-water management, greenhouse-gas emissions and air pollution.[9][10] Estonia and China have well-established oil shale industries, and Brazil, Germany, Israel and Russia also utilize oil shale.
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Oil shale, an organic-rich sedimentary rock, belongs to the group of sapropel fuels.[11] It does not have a definite geological definition nor a specific chemical formula, and its seams do not always have discrete boundaries. Oil shales vary considerably in their mineral content, chemical composition, age, type of kerogen, and depositional history.[12] Oil shale differs from bitumen-impregnated rocks (oil sands and petroleum reservoir rocks), humic coals and carbonaceous shale. While oil sands originate from the biodegradation of oil, heat and pressure have not (yet) transformed the kerogen in oil shale into petroleum.[2][13][14]
Oil shale contains a lower percentage of organic matter than coal. In commercial grades of oil shale the ratio of organic matter to mineral matter lies approximately between 0.75:5 and 1.5:5. At the same time, the organic matter in oil shale has an atomic ratio of hydrogen to carbon (H/C) approximately 1.2 to 1.8 times lower than for crude oil and about 1.5 to 3 times higher than for coals.[2][11][15] The organic components of oil shale derive from a variety of organisms, such as the remains of algae, spores, pollen, plant cuticles and corky fragments of herbaceous and woody plants, and cellular debris from other aquatic and land plants.[2][16] Some deposits contain significant fossils; Germany's Messel Pit has the status of a Unesco World Heritage Site. The mineral matter in oil shale includes various fine-grained silicates and carbonates.[6][11]
Geologists can classify oil shales on the basis of their composition as carbonate-rich shales, siliceous shales, or cannel shales.[17] Another classification, known as the van Krevelen diagram, assigns kerogen types, depending on the hydrogen, carbon, and oxygen content of oil shales' original organic matter.[12] The most commonly used classification of oil shales, developed between 1987 and 1991 by Adrian C. Hutton of the University of Wollongong, adapts petrographic terms from coal terminology. This classification designates oil shales as terrestrial, lacustrine (lake-bottom-deposited), or marine (ocean bottom-deposited), based on the environment of the initial biomass deposit.[6][18] Hutton's classification scheme has proven useful in estimating the yield and composition of the extracted oil.[2]
As with all oil and gas resources, analysts distinguish between oil shale resources and oil shale reserves. "Resources" refers to all oil shale deposits, while "reserves", represents those deposits from which producers can extract oil shale economically using existing technology. Since extraction technologies develop continuously, planners can only estimate the amount of recoverable kerogen.[6][19] Although resources of oil shale occur in many countries, only 33 countries possess known deposits of possible economic value.[20][21] Well-explored deposits, potentially classifiable 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, southern Mongolia and Russia. These deposits have given rise to expectations of yielding at least 40 liters of shale oil per tonne of oil shale, using the Fischer Assay.[6][12]
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 exceeds the world's proven conventional oil reserves, estimated at 1.317 trillion barrels (209.4×109 m3), as of 1 January 2007.[22] The largest deposits in the world occur in the United States in the Green River Formation, which covers portions of Colorado, Utah, and Wyoming; about 70% of this resource lies on land owned or managed by the United States federal government.[23] 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.[20] These figures remain tentative, with exploration or analysis of several deposits still outstanding.[2][6] Professor Alan R. Carroll of University of Wisconsin–Madison regards the Upper Permian lacustrine oil-shale deposits of northwest China, absent from previous global oil shale assessments, as comparable in size to the Green River Formation.[24]
Humans have used oil shale as a fuel since prehistoric times, since it generally burns without any processing.[25] Britons of the Iron Age also used to polish it and form it into ornaments.[26] Modern industrial mining of oil shale began in 1837 in Autun, France, followed by exploitation in Scotland, Germany, and several other countries.[2][27] Operations during the 19th century focused on the production of kerosene, lamp oil, and paraffin; these products helped supply the growing demand for lighting that arose during the Industrial Revolution.[28] Fuel oil, lubricating oil and grease, and ammonium sulfate were also produced.[29] The European oil-shale industry expanded immediately before World War I due to limited access to conventional petroleum resources and to the mass production of automobiles and trucks, which accompanied an increase in gasoline consumption.
Although the Estonian and Chinese oil-shale industries continued to grow after World War II, most other countries abandoned their projects due to high processing-costs and the availability of cheaper petroleum.[2][6][27][30] Following the 1973 oil crisis, world production of oil shale reached a peak of 46 million tonnes in 1980 before falling to about 16 million tonnes in 2000, due to competition from cheap conventional petroleum in the 1980s.[9][20] On 2 May 1982, known in some circles as "Black Sunday", Exxon canceled its US$5 billion Colony Shale Oil Project near Parachute, Colorado because of low oil-prices and increased expenses, laying off more than 2,000 workers and leaving a trail of home-foreclosures and small-business bankruptcies.[31] In 1986, President Ronald Reagan signed into law the Consolidated Omnibus Budget Reconciliation Act of 1985 which among other things abolished the United States' Synthetic Liquid Fuels Program.[4]
The global oil-shale industry began to revive at the beginning of the 21st century. In 2003, an oil-shale development program restarted in the United States. Authorities introduced a commercial leasing program permitting the extraction of oil shale and oil sands on federal lands in 2005, in accordance with the Energy Policy Act of 2005.[32][33]
As of 2008[update], industry uses oil shale in Brazil, China, Estonia and to some extent in Germany, Israel, and Russia. Several additional countries started assessing their reserves or had built experimental production plants, while others had phased out their oil shale industry.[2] Oil shale serves 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 for use in chemical industries in China, Estonia, and Russia.[2][30][34][35] As of 2009[update], 80% of oil shale used globally is extracted in Estonia.[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 plan to construct power plants fired by oil shale, while Canada and Turkey plan to burn oil shale along with coal for power generation.[2][20][37] Oil shale serves 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]
Most exploitation of oil shale involves mining followed by shipping elsewhere, after which one can burn the shale directly to generate electricity, or undertake further processing. The most common methods of surface mining involve open pit mining and strip mining. These procedures remove most of the overlying material to expose the deposits of oil shale, and become practical when the deposits occur near the surface. Underground mining of oil shale, which removes less of the overlying material, employs the room-and-pillar method.[39]
The extraction of the useful components of oil shale usually takes place above ground (ex-situ processing), although several newer technologies perform this underground (on-site or in-situ processing).[40] In either case, the chemical process of pyrolysis converts the kerogen in the oil shale to shale oil (synthetic crude oil) and oil shale gas. Most conversion technologies involve heating shale in the absence of oxygen to a temperature at which kerogen decomposes (pyrolyses) into gas, condensable oil, and a solid residue. This usually takes place between 450 °C (842 °F) and 500 °C (932 °F).[19] The process of decomposition begins at relatively low temperatures (300 °C/570 °F), but proceeds more rapidly and more completely at higher temperatures.[41]
In-situ processing involves heating the oil shale underground. Such technologies can potentially extract more oil from a given area of land than ex-situ processes, since they can access the material at greater depths than surface mines can.[42]
Several companies have patented methods for in-situ retorting. However, most of these methods remain in the experimental phase. One can distinguish true in-situ processes (TIS) and modified in-situ processes (MIS). True in-situ processes do not involve mining the oil shale. Modified in-situ processes involve removing part of the oil shale and bringing it to the surface for modified in-situ retorting in order to create permeability for gas flow in a rubble chimney. Explosives rubblize the oil-shale deposit.[43]
Hundreds of patents for oil shale retorting technologies exist;[44] however, only a few dozen have undergone testing. As of 2006, only four technologies remained in commercial use: Kiviter, Galoter, Fushun, and Petrosix.[45]
Industry can use oil shale 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 occur in Estonia, which has an installed capacity of 2,967 megawatts (MW), Israel (12.5 MW), China (12 MW), and Germany (9.9 MW).[20][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.[2][6] 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 served for uranium production in Sillamäe, Estonia, and between 1950 and 1989 Sweden used alum shale for the same purposes.[6] Oil shale gas has served as a substitute for natural gas, but as of 2009[update], producing oil shale gas as a natural-gas substitute remained economically infeasible.[47][48]
The shale oil derived from oil shale does not directly substitute for crude oil in all applications. It may contain higher concentrations of olefins, oxygen, and nitrogen than conventional crude oil.[4] Some shale oils may have higher sulfur or arsenic content. By comparison with West Texas Intermediate, the benchmark standard for crude oil in the futures-contract market, the Green River shale oil sulfur content ranges from near 0% to 4.9% (in average 0.76%), where West Texas Intermediate's sulfur content has a maximum of 0.42%.[49] The sulfur content in shale oil from Jordan's oil shales may rise even up to 9.5%.[50] The arsenic content, for example, becomes an issue for Green River formation oil shale. The higher concentrations of these materials means that the oil must undergo considerable upgrading (hydrotreating) before serving as oil-refinery feedstock.[17] Above-ground retorting processes tended to yield a lower API gravity shale oil than the in situ processes. Shale oil serves best for producing middle-distillates such as kerosene, jet fuel, and diesel fuel. Worldwide demand for these middle distillates, particularly for diesel fuels, increased rapidly in the 1990s and 2000s.[4][51] However, appropriate refining processes equivalent to hydrocracking can transform shale oil into a lighter-range hydrocarbon (gasoline).[4]
| NYMEX light-sweet crude oil in US dollars, 2005 to Mar 2008 (not adjusted for inflation) | 2005 to Nov 2008 |
During the early 20th century, the crude-oil industry expanded. Since then, the various attempts to develop oil shale deposits have succeeded only when the cost of shale-oil production in a given region comes in below the price of crude oil or its other substitutes.[52] According to a survey conducted by the RAND Corporation, the cost of producing a barrel of oil at a surface retorting complex in the United States (comprising a mine, retorting plant, upgrading plant, supporting utilities, and spent shale reclamation), would range between US$70–95 ($440–600/m3, adjusted to 2005 values). This estimate considers varying levels of kerogen quality and extraction efficiency. In order to run a profitable operation, the price of crude oil would need to remain above these levels. The analysis also discusses the expectation that processing costs would drop after the establishment of the complex. The hypothetical unit would see a cost reduction of 35–70% after producing its first 500 million barrels (79×106 m3). Assuming an increase in output of 25 thousand barrels per day (4.0×103 m3/d) during each year after the start of commercial production, RAND predicts the costs would decline to $35–48 per barrel ($220–300/m3) within 12 years. After achieving the milestone of 1 billion barrels (160×106 m3), its costs would decline further to $30–40 per barrel ($190–250/m3).[34][39] Some commentators compare the proposed American oil-shale industry to the Athabasca oil-sands industry (the latter enterprise generated over one million barrels of oil per day in late 2007), stating that "the first-generation facility is the hardest, both technically and economically".[53][54]
Royal Dutch Shell has announced that its in situ extraction technology in Colorado could become competitive at prices over $30 per barrel ($190/m3), while other technologies at full-scale production assert profitability at oil prices even lower than $20 per barrel ($130/m3).[43][55][56] To increase efficiency when retorting oil shale, researchers have proposed and tested several co-pyrolysis processes.[57][58][59][60][61]
A 1972 publication in the journal Pétrole Informations (ISSN 0755-561X) compared shale-based oil production unfavorably with the liquefaction of coal. The article portrayed coal liquefaction as less expensive, generating more oil, and creating fewer environmental impacts than extraction from oil shale. It cited a conversion ration of 650 litres (170 U.S. gal; 140 imp gal) of oil per one ton of coal, as against 150 litres (40 U.S. gal; 33 imp gal) of shale oil per one ton of oil shale.[27]
A critical measure of the viability of oil shale as an energy source lies in the ratio of the energy produced by the shale to the energy used in its mining and processing, a ratio known as "Energy Returned on Energy Invested" (EROEI). A 1984 study estimated the EROEI of the various known oil-shale deposits as varying between 0.7–13.3[62] although known oil-shale extraction development projects assert an EROI between 3 to 10. Royal Dutch Shell has reported an EROEI of three to four on its in situ development, Mahogany Research Project.[55][63][64] The water needed in the oil shale retorting process offers an additional economic consideration: this may pose a problem in areas with water scarcity.
Mining oil shale involves a number of environmental impacts, more pronounced in surface mining than in underground mining. They include acid drainage induced by the sudden rapid exposure and subsequent oxidation of formerly buried materials, the introduction of metals into surface-water and groundwater, increased erosion, sulfur-gas emissions, and air pollution caused by the production of particulates during processing, transport, and support activities.[9][10] In 2002, about 97% of air pollution, 86% of total waste and 23% of water pollution in Estonia came from the power industry, which uses oil shale as the main resource for its power production.[65]
Oil-shale extraction can damage the biological and recreational value of land and the ecosystem in the mining area. Combustion and thermal processing generate waste material. In addition, the atmospheric emissions from oil shale processing and combustion include carbon dioxide, a greenhouse gas. Environmentalists oppose production and usage of oil shale, as it creates even more greenhouse gases than conventional fossil fuels.[66] Section 526 of the Energy Independence And Security Act prohibits United States government agencies from buying oil produced by processes that produce more greenhouse gas emissions than would traditional petroleum.[67][68] Experimental in situ conversion processes and carbon capture and storage technologies may reduce some of these concerns in the future, but at the same time they may cause other problems, including groundwater pollution.[69]
Some commentators have expressed concerns over the oil shale industry's use of water. In 2002, the oil shale-fired power industry used 91% of the water consumed in Estonia.[65] Depending on technology, above-ground retorting uses between one and five barrels of water per barrel of produced shale-oil.[39][70][71][72][73] A 2007 programmatic environmental impact statement issued by the US Bureau of Land Management stated that surface mining and retort operations produce two to ten US gallons (1.5–8 imperial gallons or 8–38 L) of wastewater per tonne of processed oil shale.[70] In situ processing, according to one estimate, uses about one-tenth as much water.[74]
Water concerns become particularly sensitive issues in arid regions, such as the western US and Israel's Negev Desert, where plans exist to expand oil-shale extraction despite a water shortage.[75]
Environmental activists, including members of Greenpeace, have organized strong protests against the oil shale industry. In one result, Queensland Energy Resources put the proposed Stuart Oil Shale Project in Australia on hold in 2004.[9][76][77][78]
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