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Oil shale, also known as kerogen shale, is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons called shale oil (not to be confused with tight oil—crude oil occurring naturally in shales) can be produced. Shale oil is a substitute for conventional crude oil; however, extracting shale oil from oil shale is more costly than the production of conventional crude oil both financially and in terms of its environmental impact.〔 Deposits of oil shale occur around the world, including major deposits in the United States. Estimates of global deposits range from of oil in place.〔Dyni (2010), pp. 101–102〕〔IEA (2010), p. 165〕 Heating oil shale to a sufficiently high temperature causes the chemical process of pyrolysis to yield a vapor. Upon cooling the vapor, the liquid shale oil—an unconventional oil—is separated from combustible oil-shale gas (the term ''shale gas'' can also refer to gas occurring naturally in shales). Oil shale can also be burned directly in furnaces as a low-grade fuel for power generation and district heating or used as a raw material in chemical and construction-materials processing.〔 〕 Oil shale gains attention as a potential abundant source of oil whenever the price of crude oil rises.〔 〕〔 〕 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.〔〔 Estonia and China have well-established oil shale industries, and Brazil, Germany, and Russia also utilize oil shale.〔Dyni (2010), pp. 103–122〕 General composition of oil shales constitutes inorganic matrix, bitumens, and kerogen. Oil shales differ from oil-''bearing'' shales, shale deposits that contain petroleum (tight oil) that is sometimes produced from drilled wells. Examples of oil-''bearing'' shales are the Bakken Formation, Pierre Shale, Niobrara Formation, and Eagle Ford Formation. == Geology == (詳細はsapropel fuels.〔 〕 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 and not all oil shales would necessarily be classified as shales in the strict sense.〔EIA (2006), p. 53〕〔 〕 According to the petrologist Adrian C. Hutton of the University of Wollongong, oil shales are not "geological nor geochemically distinctive rock but rather 'economic' term."〔 〕 Their common feature is low solubility in low-boiling organic solvents and generation of liquid organic products on thermal decomposition.〔 〕 Oil shale differs from bitumen-impregnated rocks (oil sands and petroleum reservoir rocks), humic coals and carbonaceous shale. While oil sands do originate from the biodegradation of oil, heat and pressure have not (yet) transformed the kerogen in oil shale into petroleum, that means that its maturation does not exceed early mesocatagenetic.〔〔 (reprinted ) December 2009 in ''European Geologist'' 28, pp. 5–8 〕〔 〕 General composition of oil shales constitutes inorganic matrix, bitumens, and kerogen. While the bitumen portion of oil shales is soluble in carbon disulfide, kerogen portion is insoluble in carbon disulfide and can contain iron, vanadium, nickel, molybdenum, and uranium.〔 〕 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.〔〔Dyni (2010), p. 94〕〔van Krevelen (1993), p. ?〕 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.〔〔 〕 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.〔〔 Inorganic matrix can contain quartz, feldspars, clays (mainly illite and chlorite), carbonates (calcite and dolomites), pyrite and some other minerals.〔 Geologists can classify oil shales on the basis of their composition as carbonate-rich shales, siliceous shales, or cannel shales.〔Lee (1990), p. 10〕 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.〔 The most commonly used classification of oil shales, developed between 1987 and 1991 by Adrian C. Hutton, 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.〔 Known oil shales are predominantly aquatic (marine, lacustrine) origin.〔〔 Hutton's classification scheme has proven useful in estimating the yield and composition of the extracted oil.〔Dyni (2010), p. 95〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Oil shale」の詳細全文を読む スポンサード リンク
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