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Energy Minerals Division

A Division of the American Association of Petroleum Geologists

Oil Shale

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Oil shales ranging from Cambrian to Tertiary in age occur in many parts of the world. Deposits range from small occurrences of little or no economic value to those of enormous size that occupy thousands of square miles and contain many billions of barrels of potentially extractable shale oil.  Total world resources of oil shale are conservatively estimated at 2.6 trillion barrels.  However, petroleum-based crude oil is cheaper to produce today than shale oil because of the additional costs of mining and extracting the energy from oil shale.  Because of these higher costs, only a few deposits of oil shale are currently being exploited in China, Brazil, and Estonia.  However, with the continuing decline of petroleum supplies, accompanied by increasing costs of petroleum-based products, oil shale presents opportunities for supplying some of the fossil energy needs of the world in the years ahead. 

Definition of oil shale

Most oil shales are fine-grained sedimentary rocks containing relatively large amounts of organic matter from which significant amounts of shale oil and combustible gas can be extracted by destructive distillation.  Included in most definitions of "oil shale", either stated or implied, is the potential for the profitable extraction of shale oil and combustible gas or for burning as a fuel.  Oil shale differs from coal whereby the organic matter in coal has a lower atomic H:C ratio and the OM:MM ratio of coal is usually greater than 4.75:5.

Origin of oil shale

Oil shales were deposited in a wide variety of environments including freshwater to saline ponds and lakes, epicontinental marine basins and related subtidal shelves.  They were also deposited in shallow ponds or lakes associated with coal-forming peat in limnic and coastal swamp depositional environments. It is not surprising, therefore, that oil shales exhibit a wide range in organic and mineral composition.  Most oil shales contain organic matter derived from varied types of marine and lacustrine algae, with some debris of land plants, depending upon the depositional environment and sediment sources. 

History of the oil shale industry

The use of oil shale can be traced back to ancient times.  By the seventeenth century, oil shales were being exploited in several countries. One of the interesting oil shales is the Swedish alum shale of Cambrian and Ordovician age that is noted for its alum content and high concentrations of metals including uranium and vanadium.  As early as 1637, the alum shales were roasted over wood fires to extract potassium aluminum sulfate, a salt used in tanning leather and for fixing colors in fabrics.  Late in the 1800s, the alum shales were retorted on a small scale for hydrocarbons.  Production continued through World War II but ceased in 1966 because of the availability of cheaper supplies of petroleum crude oil. 

An oil shale deposit at Autun, France, was exploited commercially as early as 1839.  The Scottish oil shale industry began about 1859, the year that Colonel Drake drilled his pioneer well at Titusville, Pennsylvania.  As many as 20 beds of oil shale were mined at different times.  Mining continued during the 1800s and by 1881 oil shale production had reached one million metric tons per year.  With the exception of the World War II years, between 1 and 4 million metric tons of oil shale were mined yearly in Scotland from 1881 to 1955 when production began to decline, then ceased in 1962.  Canada produced some shale oil from deposits in New Brunswick and Ontario in the mid-1800s.

Common products made from oil shale from these early operations were kerosene and lamp oil, paraffin, fuel oil, lubricating oil and grease, and amonium sulfate.

With the introduction of the mass production of automobiles and trucks in the early 1900s, the supposed shortage of gasoline encouraged the exploitation of oil shale deposits for transportation fuels.  Many companies were formed to develop the oil shale deposits of the Green River Formation in western United States, especially in Colorado.  Oil placer claims were filed by the thousands on public lands in western United States.  The Mineral Leasing Act of 1920 removed oil shale and certain other fossil fuels and minerals on public lands administered by the Federal Government from the status of locatable to leaseable minerals. 

Several oil shale leases on Federal lands in Colorado and Utah were issued to private companies in the 1970s.  Large-scale mine facilities were developed on the properties and experimental underground "modified in situ" retorting was carried out on one of the lease tracts.  However, all work has ceased and the leases have been relinquished to the Federal Government.  Unocal operated the last large-scale experimental mining and retorting facility in western United States from 1980 until its closure in 1991.  Unocal produced 4.5 million barrels of oil from oil shale averaging 34 gallons of shale oil per ton of rock over the life of the project.

Recoverable resources

The amount of shale oil that can be recovered from a given deposit depends upon many factors.  Some deposits or portions thereof, such as large areas of the Devonian black shales in eastern United States, may be too deeply buried to economically mine in the foreseeable future.  Surface land uses may greatly restrict the availability of some oil shale deposits for development, especially those in the industrial western countries. The bottom line in developing a large oil shale industry will be governed by the price of petroleum-based crude oil.  When the price of shale oil is comparable to that of crude oil because of diminishing resources of crude, then shale oil may find a place in the world fossil energy mix.

For a complete version of the above, see the Committee’s Annual Report (May 2013) on the EMD Members Only page (log-in required).

If you would like to learn more about oil shales or to receive information on oil shales, or on activities of the EMD Oil Shale Committee, join the EMD. If you are already an EMD Member, see “Members Only Pagehttp://emd.aapg.org/members_only/oil_shale/index.cfm for updates on oil shales, for links to technical information on oil shales, and for related environmental information that may impact oil shales.

For further information on this committee’s activities, go to the Members’ Only Web page or contact:

Alan Burnham, Chair
Phone: (201) 207-7919

AAPG Explorer

August 2010: Oil Shales Making Cautious Progress
EMD Column by Jeremy Boak
November 2009: Needed: Resourceful technology Lots of Potential, Lots of Hurdles
EMD Column by Fran Hein
May 2006: Will Oil Shale Be a Major Player?
EMD Column by John R. Dyni and Ronald C. Johnson