Changes

The potential of an oil shale as a source of energy depends on the economic recoverability of oil (and gas) from it. The lower limit of the oil yield for an oil shale to be considered potentially economic now ranges between 10 and 15 gal of shale oil per ton, but the development of new mining and processing technology for the oil shale or a substantial increase of the price of oil may make oil shales with lower oil yields economically attractive in the future. At present, only the oil shales with the higher oil yields are used to obtain shale oil, about 25% of the total world oil shales mined. The remaining 75% is mainly used as a solid fuel in the generation of electricity and heat (69%) and for the production of synthetic domestic gas, cement, and speciality chemical products (6%).  

The potential of an oil shale as a source of energy depends on the economic recoverability of oil (and gas) from it. The lower limit of the oil yield for an oil shale to be considered potentially economic now ranges between 10 and 15 gal of shale oil per ton, but the development of new mining and processing technology for the oil shale or a substantial increase of the price of oil may make oil shales with lower oil yields economically attractive in the future. At present, only the oil shales with the higher oil yields are used to obtain shale oil, about 25% of the total world oil shales mined. The remaining 75% is mainly used as a solid fuel in the generation of electricity and heat (69%) and for the production of synthetic domestic gas, cement, and speciality chemical products (6%).  

Oil shales are known from many countries throughout the world. They range in age from [[Proterozoic]] to [[Tertiary]], but not all are potential commercial sources of energy. Russell<ref name=Russell_1990>Russell, P. L., 1990, Oil shales of the world, their origin, occurrence and exploitation: Oxford, Pergamon Press, 753 p.</ref> discusses the occurrence of oil shales in 51 countries (see also Duncan and Swanson<ref name=Duncanandswanson_1965>Duncan, D. C., and V. E. Swanson, 1965, Organic rich shale of the United States and world land areas: [http://pubs.usgs.gov/circ/1965/0523/report.pdf U.S. Geological Survey Circular 523], 30 p.</ref> and Office of Technology Assessment<ref name=Congress_1980>Congress of the United States, Office of Technology Assessment, 1980, [https://www.princeton.edu/~ota/disk3/1980/8004_n.html An assessment of oil shale technologies], 517 p.</ref>). Dyni<ref name=Dyni2003>Dyni, J. R. 2003 Geology and resources of some world oil-shale deposits. Oil Shale, v. 20, p. 93-252.</ref> lists 36 countries containing oil-shale deposits in a table with their corresponding estimates of in-place shale-oil resources and discusses the 14 countries with the largest of these deposits. The most important oil-shale deposits are those of the [[Eocene]] [[Green River Formation]] in the states of Colorado, Utah, and Wyoming in the United States and those of the [[Permian]] [[Irati Shale]] of southern Brazil. Other significant oil-shale deposits are known in Estonia, China, Russa, Australia, Canada, Morocco, Israel, and Jordan. More than 40 other countries are reported to have oil-shale deposits, but few of them are, as of 2005, considered as possible commercial sources of energy.

Oil shales are known from many countries throughout the world. They range in age from [[Proterozoic]] to [[Tertiary]], but not all are potential commercial sources of energy. Russell<ref name=Russell_1990>Russell, P. L., 1990, Oil shales of the world, their origin, occurrence and exploitation: Oxford, Pergamon Press, 753 p.</ref> discusses the occurrence of oil shales in 51 countries (see also Duncan and Swanson<ref name=Duncanandswanson_1965>Duncan, D. C., and V. E. Swanson, 1965, Organic rich shale of the United States and world land areas: [http://pubs.usgs.gov/circ/1965/0523/report.pdf U.S. Geological Survey Circular 523], 30 p.</ref> and Office of Technology Assessment<ref name=Congress_1980>Congress of the United States, Office of Technology Assessment, 1980, [https://www.princeton.edu/~ota/disk3/1980/8004_n.html An assessment of oil shale technologies], 517 p.</ref>). Dyni<ref name=Dyni2003>Dyni, J. R. 2003 Geology and resources of some world oil-shale deposits. Oil Shale, v. 20, p. 93-252.</ref> lists 36 countries containing oil-shale deposits in a table with their corresponding estimates of in-place shale-oil resources and discusses the 14 countries with the largest of these deposits. The most important oil-shale deposits are those of the [[Eocene]] [[Green River Formation]] in the states of Colorado, Utah, and Wyoming in the United States and those of the [[Permian]] [[Irati Formation|Irati Shale]] of southern Brazil. Other significant oil-shale deposits are known in Estonia, China, Russa, Australia, Canada, Morocco, Israel, and Jordan. More than 40 other countries are reported to have oil-shale deposits, but few of them are, as of 2005, considered as possible commercial sources of energy.

In most countries of the world, the oil-shale deposits are insufficiently studied, and information concerning their size or the quality of the shale is, in many cases, lacking or, worse, greatly exaggerated.

In most countries of the world, the oil-shale deposits are insufficiently studied, and information concerning their size or the quality of the shale is, in many cases, lacking or, worse, greatly exaggerated.