Examples of oil-bearing shales are the Bakken Formation, Pierre Shale, Niobrara Formation, and Eagle Ford Formation. Oil shales differ also from oil-bearing shales, shale deposits that contain tight oil that is sometimes produced from drilled wells. While oil sands do originate from the biodegradation of oil, heat and pressure have not (yet) transformed the kerogen in oil shale into petroleum, which means its maturation does not exceed early mesocatagenetic. Oil shale differs from bitumen-impregnated rocks (other so-called unconventional resources such as oil sands and petroleum reservoir rocks), humic coals and carbonaceous shale. Geologists can classify oil shales on the basis of their composition as carbonate-rich shales, siliceous shales, or cannel shales. Their common defining feature is low solubility in low-boiling organic solvents and generation of liquid organic products on thermal decomposition. Hutton of the University of Wollongong, oil shales are not "geological nor geochemically distinctive rock but rather 'economic' term". 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. It does not have a definite geological definition nor a specific chemical formula, and its seams do not always have discrete boundaries. Oil shale, an organic-rich sedimentary rock, belongs to the group of sapropel fuels. Outcrop of Ordovician oil shale ( kukersite), northern Estonia
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. Shale oil is a substitute for conventional crude oil however, extracting shale oil is costlier than the production of conventional crude oil both financially and in terms of its environmental impact. Upon cooling the vapor, the liquid unconventional oil, called shale oil, is separated from combustible oil-shale gas. Heating oil shale to a sufficiently high temperature causes the chemical process of pyrolysis to yield a vapor. Oil shale can 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. Only Estonia and China have well-established oil shale industries, and Brazil, Germany, and Russia utilize oil shale to some extent.
However, the various attempts to develop oil shale deposits have had limited success. Oil shale has gained attention as a potential abundant source of oil.
A 2016 estimate of global deposits set the total world resources of oil shale equivalent of 6.05 trillion barrels (962 billion cubic metres) of oil in place. ĭeposits of oil shale occur around the world, including major deposits in the United States. Accordingly, shale oil produced from oil shale should not be confused with tight oil, which is also frequently called shale oil. Examples of oil- bearing shales are the Bakken Formation, Pierre Shale, Niobrara Formation, and Eagle Ford Formation. Oil shales differ from oil- bearing shales, shale deposits that contain petroleum ( tight oil) that is sometimes produced from drilled wells. Based on their deposition environment, oil shales are classified as marine, lacustrine and terrestrial oil shales. In addition to kerogen, general composition of oil shales constitutes inorganic substance and bitumens. Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons can be produced.
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