Oil shale

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 burnt 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] The oil shale industry is well-established in Estonia, China, and Brazil, and the United States is taking steps in that direction. At the same time oil shale mining and processing involves a number of environmental issues, such as land use, waste disposal, water use and waste water management, and air pollution.[9][10] The industry has foundered in Australia due to opposition on these grounds.
Geolog
Oil shale consists of organic-rich sedimentary rock: it belongs to the group of sapropel fuels.[11] It is differentiated from bitumen-impregnated rocks (tar sands and petroleum reservoir rocks), humic coals and carbonaceous shale. While tar sands have been created by biodegradation of oil, the kerogen in oil shales has not yet been naturally transformed into petroleum by heat and pressure.[2][12][13] Coal contains a higher percentage of organic matter than oil shale. In commercial grades of oil shale the ratio of organic matter to mineral matter is about 0.75:5 to 1.5:5. At the same time, the organic matter in oil shale has an atomic ratio of hydrogen to carbon approximately the same as for crude oil and four to five times higher than for coals.[2][11]
Oil shale does not have a definite geological definition nor a specific chemical formula. Oil shales vary considerably in their mineral content, chemical composition, age, type of kerogen, and depositional history.[14] 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][15] Some deposits contain significant fossils; Germany's Messel Pit is a Unesco World Heritage Site. The mineral matter in oil shale includes various fine-grained silicates and carbonates.[11][6]
Geologists can classify oil shales on the basis of their composition as carbonate-rich shales, siliceous shales, or cannel shales.[16] Another classification, assigning kerogen types, is based on the hydrogen, carbon, and oxygen content of oil shales' original organic matter. This classification is known as the van Krevelen diagram.[14] The most used classification of oil shales was developed between 1987 and 1991 by Adrian C. Hutton of the University of Wollongong, adapting petrographic terms from coal terminology. According to this classification, oil shales are designated as terrestrial, lacustrine (lake-bottom-deposited), or marine (ocean bottom-deposited), based on the environment where the initial biomass was deposited. [6][17] Hutton's classification scheme has proven useful in estimating the yield and composition of the extracted oil.[2]
From : http://en.wikipedia.org/wiki/Oil_shale