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Oil shale

Oil shale is a general term applied to a group of fine black to dark brown shales rich enough in bituminous material (called kerogen) to yield petroleum upon distillation. The kerogen in oil shale can be converted to oil through the chemical process of pyrolysis. During pyrolysis the oil shale is heated to 500° C in the absence of air and the kerogen is converted to oil and separated out, a process called "retorting". The US Geological Survey estimates the world supply of oil shale at 2.6 trillion barrels of which 2.1 trillion barrels is in the United States. Estonia, Russia, Brazil, and China currently mine oil shale, however production is declining due to economic and environmental factors.

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Geology

Oil shale was formed in the distant past by the simultaneous deposit of silt and organic debris on lakebeds and sea bottoms. As the raw materials accumulated, heat and pressure transformed them into a stable mixture of inorganic minerals and solidified organic sludge. However the heat and pressure were not as great as in the similar process that forms petroleum.

History

Oil shale has been used since ancient times and like coal can be used directly as a fuel. The modern use of oil shale to produce oil dates to Scotland in the 1850s. In 1847 Dr James Young[?] prepared lighting oil, lubricating oil and wax from coal. Then he moved his operations to Edinburgh where oil shale deposits were found. In 1850 he patented the process of "cracking", oil into its constituent parts. Oil from oil shale was produced in that region from 1857 until 1962 when production was cancelled due to the much lower cost of petroleum.

Estonia began exploiting its shale oil deposits in the 1920s and is currently the largest user of oil shale. Today however most of it is burnt directly to produce electricity.

Economics

The energy subsidy to produce oil from oil shale is heavy. Since the oil shale has to be mined, transported, retorted, and then disposed of at least 40% of the energy value is consumed in production. Water is also needed to add hydrogen to the oil shale oil before it can be shipped to a conventional oil refinery. The largest deposit of oil shale in the United States is in western Colorado (the Green River Shale deposits) a dry region without surplus water. The oil shale can be ground into a slurry and transported via pipeline to a more suitable pre-refining location.

Environmental Considerations

Oil shale exploitation has all the normal environmental effects from open-pit mining, the pre-refining stage to get crude oil may emit ash, pipelines must be built to an oil refinery, and the waste rock must be disposed of, rock which incidentally is a known carcinogen. Oil shale rock expands by around 30% after processing due to a popcorn effect from the heating.



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