View source for Oil shale

{{short description|Organic-rich fine-grained sedimentary rock containing kerogen}}
{{For|the scientific-technical journal|Oil Shale (journal)}}
{{Distinguish|Shale oil|Tight oil}}
{{Use dmy dates|date=October 2014}}
<!-- Although both spellings—"oil shale" and "oil-shale"—are in use, this article uses the more common spelling "oil shale" in noun forms, resorting to the use of the hyphen for compound adjectival use for clarity per [[Hyphen#Compound modifiers]] -->
{{Infobox rock
|name=Oil shale
|alternative_name=
|type=Sedimentary
|type_link=Sedimentary rock
|image=Oilshale.jpg
|caption=Combustion of oil shale
|composition={{Hlist|[[Kerogen]]|[[Quartz]]|[[Feldspar]]|<br />[[Clay]]|[[Carbonate]]|[[Pyrite]]}}
|composition_secondary={{Hlist|[[Uranium]]|[[Iron]]|[[Vanadium]]|<br />[[Nickel]]|[[Molybdenum]]}}
}}
'''Oil shale''' is an organic-rich [[Granularity|fine-grained]] [[sedimentary rock]] containing [[kerogen]] (a solid mixture of [[Organic compound|organic chemical compounds]]) from which liquid [[hydrocarbon]]s can be produced. In addition to kerogen, general composition of oil shales constitutes inorganic substance and [[bitumen]]s. Based on their deposition environment, oil shales are classified as marine, lacustrine and terrestrial oil shales.<ref name="dyni" /><ref name="hutton"/> Oil shales differ from oil-''bearing'' shales, shale deposits that contain [[petroleum]] ([[tight oil]]) that is sometimes produced from drilled wells. Examples of oil-''bearing'' shales are the [[Bakken Formation]], [[Pierre Shale]], [[Niobrara Formation]], and [[Eagle Ford Group|Eagle Ford Formation]].<ref name=WER2013/> Accordingly, shale oil produced from oil shale should not be confused with tight oil, which is also frequently called shale oil.<ref name=WER2013/><ref name=WEO2013/><ref name=reinsalu/>

A 2016 estimate of global [[Deposition (geology)|deposits]] set the total world resources of oil shale equivalent of {{convert|6.05|Toilbbl|e9m3|abbr=off}} of [[oil in place]].<ref name="wec2016 16">[[#wec2016|WEC (2016)]], p. 16</ref> Oil shale has gained attention as a potential abundant source of oil.<ref name=evi>
{{Cite report
 | title = Energy Security of Estonia
 | publisher = Estonian Foreign Policy Institute
 | date = September 2006
 | url = http://www.evi.ee/lib/Security.pdf
 | access-date =20 October 2007
 | archive-url = https://web.archive.org/web/20120108161835/http://www.evi.ee/lib/Security.pdf
 | archive-date = 8 January 2012
 | url-status = dead
}}</ref><ref name=doe>
{{Cite web
 | title = Oil Shale and Other Unconventional Fuels Activities
 | publisher = [[United States Department of Energy]]
 | url = http://energy.gov/fe/services/petroleum-reserves/naval-petroleum-reserves/oil-shale-and-other-unconventional-fuels
 | access-date =9 February 2014
}}</ref> However, the various attempts to develop oil shale deposits have had limited success. Only Estonia and China have well-established oil shale industries, and Brazil, Germany, and Russia  utilize oil shale to some extent.<ref name="wec 103">[[#wec|Dyni (2010)]], pp. 103–122</ref>

Oil shale can be [[combustion|burned]] directly in furnaces as a low-grade fuel for [[Electricity generation|power generation]] and [[district heating]] or used as a raw material in chemical and construction-materials processing.<ref name=dyni>
{{Cite journal
 | last = Dyni | first = John R.
 | title = Geology and resources of some world oil shale deposits|journal=Scientific Investigations Report 2005–5294
 | series = Scientific Investigations Report
 | publisher = [[United States Department of the Interior]], [[United States Geological Survey]]
 | year = 2006
 | doi = 10.3133/sir29955294
 | url = https://pubs.usgs.gov/sir/2005/5294/pdf/sir5294_508.pdf
 | access-date =9 July 2007
| doi-access = free
 }}</ref> Heating oil shale to a sufficiently high temperature causes the chemical process of [[pyrolysis]] to [[Yield (chemistry)|yield]] a [[vapor]]. Upon cooling the vapor, the liquid [[unconventional oil]], called [[shale oil]], is separated from [[Combustibility and flammability|combustible]] [[Oil shale gas|oil-shale gas]]. 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 of the oil shale industry|environmental impact]].<ref name=csm/> Oil-shale mining and processing raise a number of environmental concerns, such as [[land use]], [[waste management|waste disposal]], [[Water resources|water use]], [[Water pollution|waste-water management]], [[Greenhouse gas|greenhouse-gas emissions]] and [[air pollution]].<ref name="Burnham" /><ref name="openpitimpacts"/>

== Geology ==
{{Main|Oil shale geology}}
[[File:Tootuskihind läbilõige.jpg|thumb|Outcrop of [[Ordovician]] oil shale ([[kukersite]]), northern Estonia]]

Oil shale, an organic-rich sedimentary rock, belongs to the group of [[sapropel]] [[fuel]]s.<ref name=arvoots>{{Cite journal
 |last         = Ots
 |first        = Arvo
 |title        = Estonian oil shale properties and utilization in power plants
 |journal      = Energetika
 |publisher    = Lithuanian Academy of Sciences Publishers
 |volume       = 53
 |issue        = 2
 |pages        = 8–18
 |date         = 12 February 2007
 |url          = http://elibrary.lt/resursai/LMA/Energetika/2007_2/4.pdf
 |access-date  = 6 May 2011
 |archive-date = 29 October 2016
 |archive-url  = https://web.archive.org/web/20161029172128/http://elibrary.lt/resursai/LMA/Energetika/2007_2/4.pdf
 |url-status   = dead
}}</ref>  It does not have a definite geological definition nor a specific chemical formula, and its seams do not always have discrete boundaries. 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 [[shale]]s in the strict sense.<ref name="aeo2006 53">[[#aeo2006|EIA (2006)]], p. 53</ref><ref name=turkey>
{{Cite journal
 | last1 =Altun | first1 =N. E.
 | last2 =Hiçyilmaz | first2 =C.
 | last3 =Hwang | first3 =J.-Y.
 | last4 =Suat Bağci | first4 =A.
 | last5 =Kök | first5 =M. V.
 | title =Oil shales in the world and Turkey; reserves, current situation and future prospects: a review
 | journal = [[Oil Shale (journal)|Oil Shale. A Scientific-Technical Journal]]
 | publisher = Estonian Academy Publishers
 | volume = 23
 | issue =3
 | pages =211–227
 | year =2006
 | doi =10.3176/oil.2006.3.02
 | s2cid =53395288
 | url=https://www.kirj.ee/public/oilshale/oil-2006-3-2.pdf
 | issn = 0208-189X
 | access-date =16 June 2007}}
</ref>  According to the [[petrologist]] Adrian C. Hutton of the [[University of Wollongong]], oil shales are not "geological nor geochemically distinctive rock but rather 'economic' term".<ref name=hutton2>{{Cite journal
 |last         = Hutton
 |first        = Adrian C.
 |title        = Organic petrography and oil shales
 |journal      = Energeia
 |publisher    = [[University of Kentucky]]
 |volume       = 5
 |issue        = 5
 |year         = 1994
 |url          = http://www.caer.uky.edu/energeia/PDF/vol5_5.pdf
 |access-date   = 19 December 2012
 |archive-url  = https://web.archive.org/web/20131004215208/http://www.caer.uky.edu/energeia/PDF/vol5_5.pdf
 |archive-date = 4 October 2013
 |url-status     = dead
 |df           = dmy-all
}}</ref>  Their common defining feature is low [[solubility]] in low-boiling organic solvents and generation of liquid organic products on [[thermal decomposition]].<ref name=urov>
{{Cite journal
 | last1 =Urov| first1 = K.
 | last2 =Sumberg | first2 = A.
 | title = Characteristics of oil shales and shale-like rocks of known deposits and outcrops
 | journal = [[Oil Shale (journal)|Oil Shale. A Scientific-Technical Journal]]
 | publisher = Estonian Academy Publishers
 | volume = 16
 | issue = 3 Special
 | pages = 1–64
 | year = 1999
 | doi = 10.3176/oil.1999.3S
 | url= https://kirj.ee/public/oilshale/UROV.pdf
 | issn = 0208-189X
 | isbn = 978-9985-50-274-7
 | s2cid = 252572686
 | access-date =22 September 2012}}
</ref> Geologists can classify oil shales on the basis of their composition as [[carbonate]]-rich shales, [[Silicon dioxide|siliceous]] shales, or [[Cannel coal|cannel]] shales.<ref name="lee 102">[[Oil shale#lee|Lee (1990)]], p. 10</ref>

Oil shale differs from [[Organic-rich sedimentary rocks|bitumen-impregnated rocks]] (other so-called [[Unconventional (oil & gas) reservoir|unconventional]] resources such as [[oil sands]] and petroleum reservoir rocks), [[Humic substance|humic]] coals and [[carbon]]aceous shale.  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 [[Maturity (geology)|maturation]] does not exceed early [[Catagenesis (geology)|mesocatagenetic]].<ref name=urov/><ref name=geolsoc>
{{Cite journal
 | last = Nield | first =Ted
 | title = Shale of the century?
 | url = https://www.geolsoc.org.uk/Geoscientist/Archive/February-2007/Shale-of-the-Century
 | journal = [[Geoscientist (magazine)|Geoscientist]]
 | publisher = [[Geological Society of London]]
 | volume = 17
 | issue = 2
 | date =17 February 2007
 | access-date = 4 February 2018}}
</ref><ref name=cna>
{{Cite report
 | last = O'Neil | first = William D.
 | title = Oil as a strategic factor. The supply of oil in the first half of the 21st century, and its strategic implications for the U.S.
 | publisher = CNA Corporation
 | pages = 94–95
 | date =11 June 2001
 | url= http://www.analysis.williamdoneil.com/oil_as_strategic_factor.pdf
 | access-date =19 April 2008}}
</ref> Oil shales differ also from oil-bearing shales, shale deposits that contain tight oil that is sometimes produced from drilled wells. Examples of oil-bearing shales are the [[Bakken Formation]], [[Pierre Shale]], [[Niobrara Formation]], and [[Eagle Ford Group|Eagle Ford Formation]].<ref name=WER2013/> Accordingly, shale oil produced from oil shale should not be confused with tight oil, which is called also frequently shale oil.<ref name=WER2013>[[#wec2013|WEC (2013)]], p. 2.46</ref><ref name=WEO2013>[[#we02013|IEA (2013)]], p. 424</ref><ref name=reinsalu>
{{Cite journal
 | last1 = Reinsalu | first1 = Enno
 | last2 = Aarna | first2 = Indrek
 | title = About technical terms of oil shale and shale oil 
 | journal = Oil Shale. A Scientific-Technical Journal
 | volume = 32
 | issue = 4
 | year = 2015
 | pages = 291–292
 | url = https://www.kirj.ee/public/oilshale_pdf/2015/issue_4/Oil_Shale-2015-4-291-292.pdf
 | issn = 0208-189X
 | access-date = 2016-01-16
 | doi = 10.3176/oil.2015.4.01 }}
</ref>

[[File:Torbanite 2 oil shale.jpg|thumb|left|Photomicrographs showing a cannel coal (top) 100% organic matrix and a rich oil shale (bottom) with relatively low mineral content]]General composition of oil shales constitutes inorganic matrix, bitumens, and kerogen.  While the bitumen portion of oil shales is soluble in [[carbon disulfide]], the kerogen portion is insoluble in carbon disulfide and may contain [[iron]], [[vanadium]], [[nickel]], [[molybdenum]], and [[uranium]].<ref>{{Cite journal |last1=Ferriday |first1=Tim |last2=Montenari |first2=Michael |date=2016 |title=Chemostratigraphy and Chemofacies of Source Rock Analogues: A High-Resolution Analysis of Black Shale Successions from the Lower Silurian Formigoso Formation (Cantabrian Mountains, NW Spain) |url=https://www.sciencedirect.com/science/article/abs/pii/S2468517816300053 |journal=Stratigraphy & Timescales |volume=1 |pages=123–255 |doi=10.1016/bs.sats.2016.10.004 |via=Elsevier Science Direct|url-access=subscription }}</ref><ref name=yen>
{{Cite book
 | editor1-last = Teh Fu Yen
 | editor2-last = Chilingar | editor2-first = George V.
 | last = Cane | first= R.F.
 | title = Oil Shale
 | chapter= The origin and formation of oil shale
 | publisher = Elsevier
 | location = Amsterdam
 | pages = 1–12; 56
 | year = 1976
 | chapter-url = https://books.google.com/books?id=qkU7OcVkwaIC&pg=PA56
 | isbn = 978-0-444-41408-3
 | access-date = 5 June 2009}}
</ref>  Oil shale contains a lower percentage of organic matter than [[coal]]. In commercial grades of oil shale the ratio of organic matter to mineral matter lies approximately between 0.75:5 and 1.5:5. At the same time, the organic matter in oil shale has an [[atomic ratio]] of hydrogen to carbon (H/C) approximately 1.2 to 1.8&nbsp;times lower than for crude oil and about 1.5 to 3&nbsp;times higher than for coals.<ref name=arvoots/><ref name="wec 94">[[#wec|Dyni (2010)]], p. 94</ref><ref name=vankrevelen>[[#vankrevelen|van Krevelen (1993)]], p. ?</ref>  The organic components of oil shale derive from a variety of organisms, such as the remains of [[algae]], [[spore]]s, [[pollen]], [[plant cuticle]]s and corky fragments of [[Herbaceous plant|herbaceous]] and woody plants, and cellular debris from other aquatic and land plants.<ref name="wec 94"/><ref name=alali>
{{Cite conference
 |last        = Alali
 |first       = Jamal
 |title       = Jordan oil shale, availability, distribution, and investment opportunity
 |conference  = International Oil Shale Conference
 |location    = Amman, Jordan
 |url         = http://www.sdnp.jo/International_Oil_Conference/rtos-A117.pdf
 |date        = 7 November 2006
 |access-date  = 4 March 2008
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20080527234121/http://www.sdnp.jo/International_Oil_Conference/rtos-A117.pdf
 |archive-date = 27 May 2008
 |df          = dmy-all
}}</ref>  Some deposits contain significant [[fossil]]s; Germany's [[Messel pit|Messel Pit]] has the status of a UNESCO [[World Heritage Site]]. The mineral matter in oil shale includes various fine-grained [[Silicon dioxide|silicates]] and [[Carbonate mineral|carbonates]].<ref name=dyni/><ref name=arvoots/>  Inorganic matrix can contain [[quartz]], [[feldspar]], [[clay]] (mainly [[illite]] and [[chlorite]]), carbonate ([[calcite]] and [[Dolomite (mineral)|dolomite]]), [[pyrite]] and some other minerals.<ref name=yen/>

Another classification, known as the van Krevelen diagram, assigns kerogen types, depending on the [[hydrogen]], [[carbon]], and [[oxygen]] content of oil shales' original organic matter.<ref name="turkey" /> The most commonly used classification of oil shales, developed between 1987 and 1991 by Adrian C. Hutton, adapts [[Petrography|petrographic]] terms from coal terminology. This classification designates oil shales as terrestrial, lacustrine (lake-bottom-deposited), or marine (ocean bottom-deposited), based on the environment of the initial [[biomass]] deposit.<ref name="dyni" /><ref name="hutton">{{Cite journal | last = Hutton | first = A.C. | title = Petrographic classification of oil shales | journal = International Journal of Coal Geology | publisher = [[Elsevier]] | location = Amsterdam | volume = 8 | issue = 3 | pages = 203–231 | year = 1987 | doi = 10.1016/0166-5162(87)90032-2 | issn = 0166-5162}}</ref>  Known oil shales are predominantly of aquatic (marine, lacustrine) origin.<ref name="urov" /><ref name="hutton" />  Hutton's classification scheme has proven useful in estimating the yield and composition of the extracted oil.<ref name="wec 95">[[#wec|Dyni (2010)]], p. 95</ref>

== Resource ==
{{Main|Oil shale reserves}}
[[File:OilShaleFossilsEstonia.jpg|thumb|Fossils in Ordovician oil shale (kukersite), northern Estonia]]

As source rocks for most conventional [[Petroleum reservoir|oil reservoir]]s, oil shale deposits are found in all world oil provinces, although most of them are too deep to be exploited economically.<ref name="weo2010 165">[[#weo2010|IEA (2010)]], pp. 165–169</ref>  As with all oil and gas resources, analysts distinguish between oil shale resources and oil shale reserves. "Resources" refer to all oil shale deposits, while "reserves" represent those deposits from which producers can extract oil shale economically using existing technology. Since extraction technologies develop continuously, planners can only estimate the amount of recoverable kerogen.<ref name=csm>
{{Cite journal
 | last = Youngquist | first = Walter
 | title = Shale Oil – The Elusive Energy
 | journal = Hubbert Center Newsletter
 | publisher = [[Colorado School of Mines]]
 | issue = 4
 | year = 1998
 | url= http://hubbert.mines.edu/news/Youngquist_98-4.pdf
 | access-date =17 April 2008}}
</ref><ref name=dyni/> Although resources of oil shale occur in many countries, only 33&nbsp;countries possess known deposits of potential economic value.<ref name=symposium>
{{Cite journal
 | last = Brendow | first = K.
 | title = Global oil shale issues and perspectives. Synthesis of the Symposium on Oil Shale. 18–19 November, Tallinn
 | journal = [[Oil Shale (journal)|Oil Shale. A Scientific-Technical Journal]]
 | publisher = Estonian Academy Publishers
 | volume =20
 | issue =1
 | pages =81–92
 | year = 2003
 | doi = 10.3176/oil.2003.1.09
 | s2cid = 252652047
 | url=https://www.kirj.ee/public/oilshale/9_brendow_1_03.pdf
 | issn = 0208-189X
 | access-date =21 July 2007}}
</ref><ref name=china>
{{Cite journal
 | last1 =Qian | first1 =Jialin
 | last2 =Wang | first2 =Jianqiu
 | last3 =Li | first3 =Shuyuan
 | title =Oil Shale Development in China
 | journal = [[Oil Shale (journal)|Oil Shale. A Scientific-Technical Journal]]
 | publisher = Estonian Academy Publishers
 | volume =20
 | issue =3
 | pages =356–359
 | year =2003
 | doi =10.3176/oil.2003.3S.08
 | s2cid =130553387
 | url=https://www.kirj.ee/public/oilshale/9_qian_2003_3s.pdf
 | issn = 0208-189X
 | access-date =16 June 2007}}
</ref> Well-explored deposits, potentially classifiable as reserves, include the [[Green River Formation|Green River]] deposits in the [[western United States]], the Tertiary deposits in [[Queensland]], Australia, deposits in Sweden and Estonia, the El-Lajjun deposit in Jordan, and deposits in France, Germany, Brazil, China, southern Mongolia and Russia. These deposits have given rise to expectations of yielding at least 40&nbsp;liters of shale oil per tonne of oil shale, using the [[Fischer Assay]].<ref name=dyni/><ref name=turkey/>

A 2016 estimate set the total world resources of oil shale equivalent to yield of {{convert|6.05|Toilbbl|e9m3|abbr=off}} of shale oil, with the largest resource deposits in the United States accounting more than 80% of the world total resource.<ref name="wec2016 16"/>  For comparison, at the same time the world's proven [[oil reserves]] are estimated to be {{convert|1.6976|Toilbbl|abbr=off}}.<ref name="wec2016 14">[[#wec2016|WEC (2016)]], p. 14</ref> The largest deposits in the world occur in the United States in the Green River Formation, which covers portions of [[Colorado]], [[Utah]], and [[Wyoming]]; about 70% of this resource lies on land owned or managed by the United States federal government.<ref>{{Cite web
 |title        = About Oil Shale
 |url          = http://ostseis.anl.gov/guide/oilshale/index.cfm
 |publisher    = [[Argonne National Laboratory]]
 |access-date   = 20 October 2007
 |archive-url  = https://web.archive.org/web/20071013075329/http://ostseis.anl.gov/guide/oilshale/index.cfm
 |archive-date = 13 October 2007
 |url-status     = dead
 |df           = dmy-all
}}</ref> Deposits in the United States constitute more than 80% of world resources; other significant resource holders being China, Russia, and Brazil.<ref name="wec2016 16"/> The amount of economically recoverable oil shale is unknown.<ref name="weo2010 165" />

== History ==
{{Main|History of the oil shale industry}}

[[File:Production of oil shale.png|thumb|350px|right|Production of oil shale in millions of metric tons, from 1880 to 2010. Source: Pierre Allix, Alan K. Burnham.<ref name=oilfield>{{Cite journal
 | last1 = Allix
 | first1 = Pierre
 | last2 = Burnham
 | first2 = Alan K.
 | title = Coaxing Oil from Shale
 | journal = Oilfield Review
 | publisher = [[Schlumberger]]
 | date = 1 December 2010
 | issue = 4
 | volume = 22
 | page = 6
 | url = http://www.slb.com/~/media/Files/resources/oilfield_review/ors10/win10/coaxing.ashx
 | format = PDF
 | access-date = 18 April 2012
 | archive-url = https://web.archive.org/web/20150106093639/http://www.slb.com/~/media/Files/resources/oilfield_review/ors10/win10/coaxing.ashx
 | archive-date = 6 January 2015
 | url-status = dead
 }}</ref>]]
Humans have used oil shale as a fuel since prehistoric times, since it generally burns without any processing.<ref>
{{cite conference| date=21 April 1987|conference=Oil shale symposium|location=Golden, CO
 |publisher=[[United States Department of Energy]]
 |title=Non-synfuel uses of oil shale
 |osti = 6567632}}
</ref> Around 3000 BC, "rock oil" was used in [[Mesopotamia]] for road construction and making architectural adhesives.<ref name=moody>{{Cite conference | last = Moody | first = Richard | title = UK Oil and Gas Shales—Definitions and Distribution in Time and Space | conference = History of On-Shore Hydrocarbon Use in the UK | url = https://www.geolsoc.org.uk/Groups-and-Networks/Specialist-Groups/History-of-Geology-Group/~/media/shared/documents/specialist%20and%20regional%20groups/hogg/hogg_weymouth%20abstract%20book.ashx | date = 20 April 2007 | pages = 1–2 | publisher = [[Geological Society of London]] | location = [[Weymouth, Dorset|Weymouth]] | access-date = 6 September 2014}}</ref> [[Celtic Britons|Britons]] of the [[Iron Age]] used tractable oil shales to fashion [[cist]]s for burial,<ref>{{cite book |last1=Cadell |first1=Henry M |title=The Rocks of West Lothian. An Account of the Geological and Mining History of the West Lothian District |date=1925 |publisher=Oliver and Boyd |location=Edinburgh |pages=390 |edition=1st}}</ref> or just polish it to create ornaments.<ref>
{{cite web
 |last= West | first = Ian
 |title=Kimmeridge – The Blackstone – Oil Shale
 |publisher=[[University of Southampton]]
 |date=6 January 2008
 |url= http://www.southampton.ac.uk/~imw/Kimmeridge-Oil-Shale.htm
 |access-date=9 February 2014}}
</ref>

In the 10th century, the Arab physician [[Masawaih al-Mardini]] (Mesue the Younger) described a [[Shale oil extraction|method of extraction]] of oil from "some kind of bituminous shale".<ref name="art41">{{cite book | first = Robert James | last = Forbes | title = A Short History of the Art of Distillation from the Beginnings Up to the Death of Cellier Blumenthal  | year = 1970 | publisher = [[Brill Publishers]] | url = https://books.google.com/books?id=u_tui-7XXF0C&pg=PA41 | isbn = 978-90-04-00617-1 | pages = 41–42}}</ref> The first patent for extracting oil from oil shale was British Crown Patent 330 granted in 1694 to Martin Eele, Thomas Hancock and William Portlock, who had "found a way to extract and make great quantities of pitch, tarr, and oyle out of a sort of stone".<ref name=moody/><ref name="mushrush39">[[#mushrush|Mushrush (1995)]], p. 39</ref><ref name="yen56">[[#yen|Cane (1976)]], p. 56</ref>

Modern industrial mining of oil shale began in 1837 in [[Autun]], France, followed by exploitation in Scotland, Germany, and several other countries.<ref name="wec 96">[[#wec|Dyni (2010)]], p. 96</ref><ref name=laherrere>{{Cite web
 |last         = Laherrère
 |first        = Jean
 |author-link  = Jean Laherrère
 |title        = Review on oil shale data
 |publisher    = Hubbert Peak
 |year         = 2005
 |url          = http://www.hubbertpeak.com/laherrere/oilshalereview200509.pdf
 |access-date  = 17 June 2007
 |archive-date = 28 September 2007
 |archive-url  = https://web.archive.org/web/20070928004607/http://www.hubbertpeak.com/laherrere/OilShaleReview200509.pdf
 |url-status   = dead
}}</ref> Operations during the 19th century focused on the production of [[kerosene]], lamp oil, and [[Paraffin wax|paraffin]]; these products helped supply the growing demand for lighting that arose during the [[Industrial Revolution]], supplied from Scottish oil shales.<ref name="encarta1">
{{cite web
 |title=Petroleum 
 |first=Todd M. 
 |last=Doscher 
 |publisher=[[MSN Encarta]] 
 |access-date=22 April 2008 
 |url=http://encarta.msn.com/encyclopedia_761576221/petroleum.html 
 |archive-url=https://web.archive.org/web/20080421062940/http://encarta.msn.com/encyclopedia_761576221/Petroleum.html 
 |archive-date=21 April 2008 
 |url-status=dead 
 |df= dmy-all}}
</ref> Fuel oil, lubricating oil and grease, and [[ammonium sulfate]] were also produced.<ref>
{{cite web
 |url= http://www.aapg.org/about/aapg/overview/committees/emd/Articleid/26348/committee-emd-oil-shale#141872050-details
 |title= Oil Shale Committee-EMD
 |publisher=American Association of Petroleum Geologists
 |access-date= 4 February 2018}}
</ref>  Scottish production peaked in around 1913, operating 120 oil shale works,<ref>{{cite journal |last1=Cadell |first1=Henry |title=The geology of the oil-shale fields of the Lothians |journal=Transactions of the Edinburgh Geological Society |date=1901 |volume=8 |pages=116–163|doi=10.1144/transed.8.1.116 |s2cid=176768495 |url=https://zenodo.org/record/1600038 }}</ref> producing 3,332,000 tonnes of oil shale, generating around 2% of the global production of petroleum.<ref name=museum>{{cite web
 | title = A Brief History of the Scottish Shale Oil Industry
 | work = Museum of the Scottish Shale Oil Industry
 | url = http://www.scottishshale.co.uk/HistoryPages/index.html
 | access-date = 2012-07-07
 | archive-date = 25 September 2019
 | archive-url = https://web.archive.org/web/20190925175340/http://www.scottishshale.co.uk/HistoryPages/index.html
 | url-status = dead
 }}</ref> The Scottish oil-shale industry expanded immediately before [[World War I]] partly because of limited access to conventional petroleum resources and the mass production of automobiles and trucks, which accompanied an increase in gasoline consumption; but mostly because the [[British Admiralty]] required a reliable fuel source for their fleet as war in Europe loomed.

[[File:XXe - Mine des Télots - 02.jpg|thumb|[[Autun]] oil shale mines]]

Although the Estonian and Chinese oil-shale industries continued to grow after [[World War II]], most other countries abandoned their projects because of high processing costs and the availability of cheaper petroleum.<ref name="dyni" /><ref name="laherrere" /><ref name="wec 97">[[#wec|Dyni (2010)]], p. 97</ref><ref name="fushun2">
{{Cite conference
 |last        = Yin
 |first       = Liang
 |title       = Current status of oil shale industry in Fushun, China
 |conference  = International Oil Shale Conference
 |date        = 7 November 2006
 |location    = [[Amman]], Jordan
 |url         = http://www.sdnp.jo/International_Oil_Conference/rtos-A106.pdf
 |access-date  = 29 June 2007
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20070928110915/http://www.sdnp.jo/International_Oil_Conference/rtos-A106.pdf
 |archive-date = 28 September 2007
 |df          = dmy-all
}}
</ref> Following the [[1973 oil crisis]], world production of oil shale reached a peak of 46&nbsp;million tonnes in 1980 before falling to about 16&nbsp;million tonnes in 2000, because of competition from [[1980s oil glut|cheap conventional petroleum in the 1980s]].<ref name="Burnham">{{cite web
 | last = Burnham
 | first = A. K.
 | title = Slow Radio-Frequency Processing of Large Oil Shale Volumes to Produce Petroleum-like Shale Oil
 | publisher = [[Lawrence Livermore National Laboratory]]
 | date = 20 August 2003
 | url = https://e-reports-ext.llnl.gov/pdf/243505.pdf
 | id = UCRL-ID-155045
 | access-date = 28 June 2007
 | archive-url = https://web.archive.org/web/20170216041927/https://e-reports-ext.llnl.gov/pdf/243505.pdf
 | archive-date = 16 February 2017
 | url-status = dead
 }}</ref><ref name="symposium" />

On 2 May 1982, known in some circles as "Black Sunday", [[ExxonMobil|Exxon]] canceled its US$5&nbsp;billion [[Colony Shale Oil Project]] near [[Parachute, Colorado]], because of low oil prices and increased expenses, laying off more than 2,000&nbsp;workers and leaving a trail of home foreclosures and small business bankruptcies.<ref name="chronicle">
{{cite news
 | last = Collier | first = Robert
 | title = Coaxing oil from huge U.S. shale deposits
 | newspaper = [[San Francisco Chronicle]]
 | date = 4 September 2006
 | url = http://www.sfgate.com/news/article/Coaxing-oil-from-huge-U-S-shale-deposits-2489359.php
 | access-date = 19 December 2012}}
</ref>  In 1986, President [[Ronald Reagan]] signed into law the [[Consolidated Omnibus Budget Reconciliation Act of 1985]], which among other things abolished the United States' [[Synthetic Liquid Fuels Program]].<ref name="andrews">
{{cite report
 | last = Andrews
 | first = Anthony
 | title = Oil Shale: History, Incentives, and Policy
 | publisher = Congressional Research Service
 | date = 13 April 2006
 | url = https://fas.org/sgp/crs/misc/RL33359.pdf
 | access-date = 25 June 2007
}}</ref>

The global oil-shale industry began to revive at the beginning of the 21st century. In 2003, an oil-shale development program restarted in the United States. Authorities introduced a commercial leasing program permitting the extraction of oil shale and oil sands on federal lands in 2005, in accordance with the [[Energy Policy Act of 2005]].<ref name=blm>
{{cite press release
 |publisher   = Bureau of Land Management
 |url         = https://www.blm.gov/nhp/news/releases/pages/2005/pr050920_oilshale.htm
 |title       = Nominations for Oil Shale Research Leases Demonstrate Significant Interest in Advancing Energy Technology
 |date        = 20 September 2005
 |access-date  = 10 July 2007
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20080916051633/http://www.blm.gov/wo/st/en/info/newsroom/2005/september/NR_050920.html
 |archive-date = 16 September 2008
}}
</ref><ref name=anl>{{cite web
 |publisher    = Oil Shale and Tar Sands Leasing Programmatic EIS Information Center
 |url          = http://ostseis.anl.gov/eis/what/index.cfm
 |title        = What's in the Oil Shale and Tar Sands Leasing Programmatic EIS
 |access-date   = 10 July 2007
 |archive-url  = https://web.archive.org/web/20070703105351/http://ostseis.anl.gov/eis/what/index.cfm
 |archive-date = 3 July 2007
 |url-status     = dead
 |df           = dmy-all
}}</ref>

== Industry ==
{{Main|Oil shale industry}}
[[File:Shell insitu.gif|thumb|[[Royal Dutch Shell|Shell]]'s experimental ''in-situ'' oil-shale facility, Piceance Basin, Colorado, US|alt=A photograph of [[Shell Oil]]'s experimental ''in situ'' shale oil extraction facility in the [[Piceance Basin]] of northwestern [[Colorado]]. In the center of the photo, a number of oil recovery pipes lie on the ground. Several oil pumps are visible in the background.]]
{{As of|2008}}, oil shale is utilized primarily in Brazil, China, Estonia and to some extent in Germany, and Russia.  Several additional countries started assessing their reserves or had built experimental production plants, while others had phased out their oil shale industry.<ref name="wec 103"/> Oil shale serves for oil production in Estonia, Brazil, and China; for power generation in Estonia, China, and Germany; for cement production in Estonia, Germany, and China; and for use in chemical industries in China, Estonia, and Russia.<ref name="wec 103"/><ref name=fushun2/><ref name=eu/><ref name=jordan2>{{Cite report
 | last1 = Alali
 | first1 = Jamal
 | last2 = Abu Salah
 | first2 = Abdelfattah
 | last3 = Yasin
 | first3 = Suha M.
 | last4 = Al Omari
 | first4 = Wasfi
 | title = Oil Shale in Jordan
 | publisher = Natural Resources Authority of Jordan
 | year = 2006
 | url = http://www.memr.gov.jo/EchoBusV3.0/SystemAssets/PDFs/AR/MineralTR/Oil%20Shale.pdf
 | access-date = 11 June 2017
 | archive-date = 13 November 2018
 | archive-url = https://web.archive.org/web/20181113065148/http://www.memr.gov.jo/EchoBusV3.0/SystemAssets/PDFs/AR/MineralTR/Oil%20Shale.pdf
 | url-status = dead
 }}</ref>

{{As of|2009}}, 80% of oil shale used globally is [[Oil shale in Estonia|extracted in Estonia]], mainly because Estonia uses several [[Fossil fuel power station|oil-shale-fired power plants]],<ref name="eu" /><ref>
{{Cite web
 |title       = Importance of Future Oil Shale Industry Plans for Estonia
 |publisher   = Estonian Ministry of Economic Affairs and Communications
 |date        = 8 June 2009
 |url         = http://www.mkm.ee/june-8th-2009-oil-shale-conference-in-tallinn-univer/
 |access-date  = 2 September 2009
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20110716111423/http://www.mkm.ee/june-8th-2009-oil-shale-conference-in-tallinn-univer/
 |archive-date = 16 July 2011
 |df          = dmy-all
}}
</ref> which has an installed capacity of 2,967&nbsp;[[megawatt]]s (MW). By comparison, China's oil shale power plants have an installed capacity of 12&nbsp;MW, and Germany's have 9.9&nbsp;MW.<ref name="symposium" /><ref name="qian3">
{{Cite conference
 | last1 =Qian | first1 =Jialin
 | last2 =Wang | first2 =Jianqiu
 | last3 =Li | first3 =Shuyuan
 | title = One Year's Progress in the Chinese Oil Shale Business
 | publisher = [[China University of Petroleum]]
 | conference = 27th Oil Shale Symposium
 | location = [[Golden, Colorado]]
 | url= http://www.ceri-mines.org/documents/27symposium/presentations/av02-1qian.pdf
 | archive-url= https://web.archive.org/web/20110912031140/http://www.ceri-mines.org/documents/27symposium/presentations/av02-1qian.pdf
 | url-status= usurped
 | archive-date= 12 September 2011
 | date = 15 October 2007
 | access-date =6 May 2011}}
</ref>  A 470&nbsp;MW [[Attarat Power Plant|oil shale power plant in Jordan]] is under construction as of 2020.<ref>{{Cite news|last=Al-Khalidi|first=Suleiman|date=2017-03-16|title=Jordan moves ahead with $2.1 bln oil shale power plant|work=Reuters|url=https://www.reuters.com/article/jordan-energy-power-idUSL5N1GT4IF|access-date=2020-10-23}}</ref> Israel, Romania and Russia have in the past run power plants fired by oil shale but have shut them down or switched to other fuel sources such as [[natural gas]].<ref name="wec 103"/><ref name=symposium/><ref name=globes220311>
{{Cite news
 | last1 = Azulai | first1 =Yuval
 | title = We are not drying up the Dead Sea
 | newspaper= [[Globes (newspaper)|Globes]]
 | date = 22 March 2011
 | url = https://www.globes.co.il/en/article-1000632377
 | access-date =9 February 2014}}
</ref> Other countries, such as Egypt, have had plans to construct power plants fired by oil shale, while Canada and Turkey had plans to burn oil shale along with coal for power generation.<ref name=symposium/><ref name=Jordan>
{{Cite report
 | last1 =Hamarneh | first1 =Yousef
 | last2 =Alali | first2 =Jamal
 | last3 =Sawaged | first3 =Suzan
 | title =Oil Shale Resources Development In Jordan
 | location=Amman
 | publisher=Natural Resources Authority of Jordan
 | year = 1998}}
</ref> Oil shale serves as the main fuel for power generation only in Estonia, where 90.3% of country's electrical generation in 2016 was produced from oil shale.<ref name=yearbook2016>
{{cite book
 |title       = Estonian Oil Shale Industry. Yearbook 2016
 |publisher   = Eesti Energia, VKG, KKT, Tallinn University of Technology
 |editor1-last = Beger |editor1-first = Mariliis
 |year        = 2017
 |url         = https://www.vkg.ee/cms-data/upload/sise-uudised/polevkivi-aastaraamat-2016-eng-veeb.pdf
 |page        = 18
 |access-date  = 29 January 2018
 |df          = dmy-all}}
</ref>

According to the [[World Energy Council]], in 2008 the total production of shale oil from oil shale was 930,000&nbsp;tonnes, equal to {{convert|17700|oilbbl/d}}, of which China produced 375,000&nbsp;tonnes, Estonia 355,000&nbsp;tonnes, and Brazil 200,000&nbsp;tonnes.<ref name="wec 101">[[#wec|Dyni (2010)]], pp. 101–102</ref>  In comparison, production of the conventional oil and [[natural gas liquids]] in 2008 amounted 3.95&nbsp;billion tonnes or {{convert|82.1|Moilbbl/d|sigfig=3}}.<ref name="wec 59">[[#wec|Dyni (2010)]], pp. 59–61</ref>

== Extraction and processing ==
{{Main|Shale oil extraction}}
[[File:Oil shale extraction overview.png|thumb|right|alt=A vertical [[flowchart]] begins with an oil shale deposit and follows two major branches. Conventional ''ex situ'' processes, shown on the right, proceed through mining, crushing, and retorting. [[Spent shale]] output is noted. ''In situ'' process flows are shown in the left branch of the flowchart. The deposit may or may not be fractured; in either case, the deposit is retorted and the oil is recovered. The two major branches converge at the bottom of the chart, indicating that extraction is followed by [[refining]], which involves thermal and chemical treatment and [[hydrogenation]], yielding liquid fuels and useful byproducts.|Overview of shale oil extraction]]
[[File:VKG Ojamaa kaevandus.jpg|thumb|Mining of oil shale. [[Viru Keemia Grupp|VKG]] [[Ojamaa]].]]
Most exploitation of oil shale involves mining followed by shipping elsewhere, after which the shale is burned directly to generate electricity or undertakes further processing. The most common methods of mining involve [[open-pit mining]] and [[Surface mining|strip mining]]. These procedures remove most of the overlying material to expose the deposits of oil shale and become practical when the deposits occur near the surface. [[Underground mining (soft rock)|Underground mining of oil shale]], which removes less of the overlying material, employs the [[Room and pillar mining|room-and-pillar method]].<ref name=rand>
{{Cite book
 | last1 = Bartis | first1 = James T.
 | last2 =LaTourrette | first2 = Tom
 | last3 = Dixon | first3 =Lloyd
 | last4 = Peterson | first4 =D.J.
 | last5 = Cecchine | first5 = Gary
 | title = Oil Shale Development in the United States. Prospects and Policy Issues. Prepared for the National Energy Technology Laboratory of the U.S. Department of Energy
 | publisher = [[RAND Corporation]]
 | year = 2005
 | url = https://www.rand.org/pubs/monographs/2005/RAND_MG414.pdf
 | isbn = 978-0-8330-3848-7
 | access-date =29 June 2007}}
</ref>

The extraction of the useful components of oil shale usually takes place above ground (''ex-situ'' processing), although several newer technologies perform this underground (on-site or ''[[In situ|in-situ]]'' processing).<ref name=AICHE>{{Cite conference
 | last1 = Burnham
 | first1 = Alan K.
 | last2 = McConaghy
 | first2 = James R.
 | title = Comparison of the Acceptability of Various Oil Shale Processes
 | date = 16 October 2006
 | conference = 26th Oil Shale Symposium
 | location = [[Golden, Colorado]]
 | publisher = [[Lawrence Livermore National Laboratory]]
 | url = https://e-reports-ext.llnl.gov/pdf/341283.pdf
 | id = UCRL-CONF-226717
 | access-date = 23 June 2007
 | archive-url = https://web.archive.org/web/20160213164539/https://e-reports-ext.llnl.gov/pdf/341283.pdf
 | archive-date = 13 February 2016
 | url-status = dead
 }}</ref> In either case, the chemical process of [[pyrolysis]] converts the kerogen in the oil shale to shale oil ([[synthetic crude]] oil) and oil shale gas. Most conversion technologies involve heating shale in the absence of oxygen to a temperature at which kerogen decomposes (pyrolyses) into gas, condensable oil, and a solid residue. This usually takes place between {{convert|450|°C|°F|0|lk=on}} and {{convert|500|°C|°F|0|lk=on}}.<ref name=csm/> The process of decomposition begins at relatively low temperatures ({{convert|300|°C|°F|0|disp=or}}) but proceeds more rapidly and more completely at higher temperatures.<ref name=koel>
{{Cite journal
 |last=Koel|first=Mihkel
 | title=Estonian oil shale
 | journal = [[Oil Shale (journal)|Oil Shale. A Scientific-Technical Journal]]
 | publisher=Estonian Academy Publishers
 | issue=Extra
 | year=1999
 | url=https://www.kirj.ee/public/oilshale/Est-OS.htm
 | issn= 0208-189X
 | access-date=21 July 2007}}
</ref>

''In-situ'' processing involves heating the oil shale underground. Such technologies can potentially extract more oil from a given area of land than ''ex-situ'' processes, since they can access the material at greater depths than surface mines can.  Several companies have patented methods for ''in-situ'' [[retort]]ing. However, most of these methods remain in the experimental phase. Two ''in-situ'' processes could be used: true ''in-situ'' processing does not involve mining the oil shale, while modified ''in-situ'' processing involves removing part of the oil shale and bringing it to the surface for modified ''in-situ'' retorting in order to create permeability for gas flow in a rubble chimney. Explosives rubblize the oil-shale deposit.<ref name=fossilenergy>{{Cite report
 | last1=Johnson
 | first1=Harry R.
 | last2=Crawford
 | first2=Peter M.
 | last3=Bunger
 | first3=James W.
 | title=Strategic Significance of America's Oil Shale Resource. Volume II Oil Shale Resources, Technology and Economics
 | publisher=United States Department of Energy
 | date=March 2004
 | url=https://library.mines.edu/UserFiles/File/library/PDF/Archive/TEOSR_ONPOSR_strategic_significancev2.pdf
 | access-date=24 September 2017
 | archive-url=https://web.archive.org/web/20181113065148/https://library.mines.edu/UserFiles/File/library/PDF/Archive/TEOSR_ONPOSR_strategic_significancev2.pdf
 | archive-date=13 November 2018
 | url-status=dead
 }}</ref>

Hundreds of patents for oil shale retorting technologies exist;<ref name=patent>
{{Cite web
 | title= Process for the recovery of hydrocarbons from oil shale
 | publisher=FreePatentsOnline
 | url =https://www.freepatentsonline.com/4449586.html
 | access-date=3 November 2007}}
</ref> however, only a few dozen have undergone testing. By 2006, only four technologies remained in commercial use<!-- saying 'had reached the stage of commercial use' is not correct because more technologies have been in commercial use (latest one is the ATP technology used at the Stuart project); however they have dropped out from commercial use. Therefore it is correct to say how many technologies are in commercial use in exact time period-->: [[Kiviter process|Kiviter]], [[Galoter process|Galoter]], [[Fushun process|Fushun]], and [[Petrosix]].<ref name=qian>
{{Cite conference|conference=International Conference on Oil Shale: Recent Trends In Oil Shale
 |last1        = Qian
 |first1       = Jialin
 |last2       = Wang
 |first2      = Jianqiu
 |title       = World oil shale retorting technologies
 |date        = 7 November 2006
 |location    = [[Amman]], Jordan
 |url         = http://www.sdnp.jo/International_Oil_Conference/rtos-A118.pdf
 |access-date  = 29 June 2007
 |url-status  = dead
 |archive-url  = https://web.archive.org/web/20080527234146/http://www.sdnp.jo/International_Oil_Conference/rtos-A118.pdf
 |archive-date = 27 May 2008
 |df          = dmy-all
}}</ref>

== Applications and products ==
Oil shale is utilized as a fuel for thermal power-plants, burning it (like coal) to drive [[steam turbine]]s; some of these plants [[cogeneration|employ the resulting heat]] for [[district heating]] of homes and businesses. In addition to its use as a fuel, oil shale may also serve in the production of specialty [[Carbon fiber reinforced polymer|carbon fibers]], [[Adsorption|adsorbent carbons]], [[carbon black]], [[phenols]], resins, glues, tanning agents, mastic, road bitumen, cement, bricks, construction and decorative blocks, soil-additives, fertilizers, [[Mineral wool|rock-wool]] insulation, glass, and pharmaceutical products.<ref name="eu" />  However, oil shale use for production of these items remains small or only in experimental development.<ref name="dyni" /><ref name="wec 98">[[#wec|Dyni (2010)]], p. 98</ref> Some oil shales yield [[sulfur]], [[ammonia]], [[Aluminium oxide|alumina]], [[soda ash]], uranium, and [[nahcolite]] as shale-oil extraction byproducts. Between 1946 and 1952, a marine type of ''[[Basidiolichen|Dictyonema]]'' shale served for uranium production in [[Sillamäe]], Estonia, and between 1950 and 1989 Sweden used [[alum]] shale for the same purposes.<ref name=dyni/>  Oil shale gas has served as a substitute for [[natural gas]], but {{as of | 2009 | alt = as of 2009}}, producing oil shale gas as a natural-gas substitute remained economically infeasible.<ref name=proceedings>
{{Cite journal
 | last1 = Schora | first1 = F. C.
 | last2 = Tarman | first2 = P. B.
 | last3 = Feldkirchner | first3 = H. L.
 | last4 = Weil | first4 = S. A.
 | title = Hydrocarbon fuels from oil shale
 | journal = Proceedings
 | publisher = [[American Institute of Chemical Engineers]]
 | volume = 1
 | pages = 325–330
 | year = 1976
 | bibcode = 1976iece.conf..325S
 | id = A77-12662 02-44}}
</ref><ref name=ttu>{{Cite web
 | last = Valgma
 | first = Ingo
 | title = Map of oil shale mining history in Estonia
 | publisher = Mining Institute of [[Tallinn Technical University]]
 | url = http://www.ene.ttu.ee/maeinstituut/mgis/mapofhistory.htm
 | access-date = 21 July 2007
 | archive-date = 17 August 2014
 | archive-url = https://web.archive.org/web/20140817092025/http://www.ene.ttu.ee/maeinstituut/mgis/mapofhistory.htm
 | url-status = dead
 }}</ref>

The shale oil derived from oil shale does not directly substitute for crude oil in all applications. It may contain higher concentrations of [[Alkene|olefins]], oxygen, and nitrogen than conventional crude oil.<ref name="andrews" />  Some shale oils may have higher sulfur or [[arsenic]] content. By comparison with [[West Texas Intermediate]], the benchmark standard for crude oil in the [[futures contract|futures-contract]] market, the Green River shale oil sulfur content ranges from near 0% to 4.9% (in average 0.76%), where West Texas Intermediate's sulfur content has a maximum of 0.42%.<ref name="dyni2">
{{cite journal
 |last1= Dyni | first1= John R.
 |title= Distribution and origin of sulfur in Colorado oil shale
 |date= 1 April 1983
 |publisher= U.S. Geological Survey
 |journal = 16th Oil Shale Symposium Proceedings
 |pages= 144–159
 |id=CONF-830434-
 | osti= 5232531
 }}
</ref> The sulfur content in shale oil from Jordan's oil shales may be as high as 9.5%.<ref>
{{cite journal
 |last1 = Al-Harahsheh | first1 = Adnan
 |last2 = Al-Otoom | first2 = Awni Y.
 |last3 = Shawabkeh | first3 = Reyad A.
 |title= Sulfur distribution in the oil fractions obtained by thermal cracking of Jordanian El-Lajjun oil Shale
 |date=16 October 2003
 |journal = Energy
 |volume = 30
 |pages = 2784–2795
 |publication-date = November 2005
 |doi= 10.1016/j.energy.2005.01.013
 |issue= 15
}}
</ref>  The arsenic content, for example, becomes an issue for Green River formation oil shale. The higher concentrations of these materials means that the oil must undergo considerable upgrading ([[Hydrodesulfurization|hydrotreating]]) before serving as [[oil refinery|oil-refinery]] feedstock.<ref name="lee 6">[[#lee|Lee (1990)]], p. 6</ref>  Above-ground retorting processes tended to yield a lower [[API gravity]] shale oil than the ''in situ'' processes. Shale oil serves best for producing middle-[[Distillation|distillates]] such as [[kerosene]], [[jet fuel]], and [[diesel fuel]]. Worldwide demand for these middle distillates, particularly for diesel fuels, increased rapidly in the 1990s and 2000s.<ref name=andrews/><ref>
{{cite web
 |date=4 May 2006
 |publisher=[[United States House of Representatives]]
 |title= Statement Of Daniel Yergin, Chairman of Cambridge Energy Research Associates, Before The Committee On Energy And Commerce/U.S. House Of Representatives
 |url= http://www.gpo.gov/fdsys/pkg/CHRG-109hhrg29386/html/CHRG-109hhrg29386.htm
 |access-date=19 December 2012}}
</ref>  However, appropriate refining processes equivalent to [[Cracking (chemistry)|hydrocracking]] can transform shale oil into a lighter-range hydrocarbon ([[gasoline]]).<ref name=andrews/>

== Economics ==
{{PanoViewer|Oil shale - from research to reality 03. Enefit280 plant, view of the plant.jpg|360° panoramic view of a Enefit280 plant in [[Estonia]], that processes 280 tonnes of oil shale in an hour}}
{{Main|Oil shale economics}}
The various attempts to develop oil shale deposits have succeeded only when the cost of shale-oil production in a given region comes in below the price of crude oil or its other substitutes ([[Break-even (economics)|break-even price]]). According to a 2005 survey, conducted by the [[RAND Corporation]], the cost of producing a barrel of oil at a surface retorting complex in the United States (comprising a mine, retorting plant, [[upgrader|upgrading plant]], supporting utilities, and spent shale reclamation), would range between [[US dollars|US$]]70–95 ($440–600/m<sup>3</sup>, adjusted to 2005 values). This estimate considers varying levels of kerogen quality and extraction efficiency. In order to run a profitable operation, the price of crude oil would need to remain above these levels. The analysis also discussed the expectation that processing costs would drop after the establishment of the complex. The hypothetical unit would see a cost reduction of 35–70% after producing its first {{convert|500|Moilbbl|abbr=off}}. Assuming an increase in output of {{convert|25|koilbbl/d}} during each year after the start of commercial production, RAND predicted the costs would decline to $35–48 per barrel ($220–300/m<sup>3</sup>) within 12 years. After achieving the milestone of {{convert|1|Goilbbl|abbr=off}}, its costs would decline further to $30–40 per barrel ($190–250/m<sup>3</sup>).<ref name="eu">
{{cite report
 |publisher   = European Academies Science Advisory Council
 |url         = https://www.easac.org/fileadmin/PDF_s/reports_statements/Study.pdf
 |title       = A study on the EU oil shale industry viewed in the light of the Estonian experience. A report by EASAC to the Committee on Industry, Research and Energy of the European Parliament
 |last1       = Francu
 |first1      = Juraj
 |last2       = Harvie
 |first2      = Barbra
 |last3       = Laenen
 |first3      = Ben
 |last4       = Siirde
 |first4      = Andres
 |last5       = Veiderma
 |first5      = Mihkel
 |pages       = 12–13; 18–19; 23–24; 28
 |date        = May 2007
 |access-date  = 21 June 2010
 |url-status  = dead
 |archive-url  = https://web.archive.org/web/20110726011345/http://www.easac.org/fileadmin/PDF_s/reports_statements/Study.pdf
 |archive-date = 26 July 2011
 |df          = dmy-all
}}
</ref><ref name="rand" /> In 2010, the [[International Energy Agency]] estimated, based on the various pilot projects, that investment and operating costs would be similar to those of [[Athabasca oil sands|Canadian oil sands]], that means would be economic at prices above $60 per barrel at current costs.  This figure does not account [[carbon pricing]], which will add additional cost.<ref name="weo2010 165" /> According to the New Policies Scenario introduced in its [[World Energy Outlook|World Energy Outlook 2010]], a price of $50 per tonne of emitted {{CO2}} adds additional $7.50 cost per barrel of shale oil.<ref name="weo2010 165" /> As of November 2021, the price of tonne of {{CO2}} exceeded $60.

A 1972 publication in the journal ''Pétrole Informations'' ({{ISSN|0755-561X}}) compared shale-based oil production unfavorably with [[coal liquefaction]]. The article portrayed coal liquefaction as less expensive, generating more oil, and creating fewer environmental impacts than extraction from oil shale. It cited a conversion ratio of {{convert|650|L|U.S.gal impgal}} of oil per one [[ton]] of coal, as against {{convert|150|L|U.S.gal impgal}} of shale oil per one ton of oil shale.<ref name="laherrere" />

A critical measure of the viability of oil shale as an energy source lies in the ratio of the energy produced by the shale to the energy used in its mining and processing, a ratio known as "[[energy return on investment]]" (EROI). A 1984 study estimated the EROI of the various known oil-shale deposits as varying between 0.7–13.3,<ref name="science2">
{{Cite journal
 | last1 = Cleveland | first1 = Cutler J.
 | last2 = Costanza | first2 = Robert
 | last3 = Hall | first3 = Charles A. S.
 | last4 = Kaufmann | first4 = Robert
 | title =Energy and the U.S. Economy: A Biophysical Perspective
 | journal = [[Science (journal)|Science]]
 | publisher = [[American Association for the Advancement of Science]]
 | volume = 225
 | issue = 4665
 | pages =890–897
 | date = 31 August 1984
 | issn = 0036-8075
 | doi =10.1126/science.225.4665.890
 | pmid =17779848|bibcode = 1984Sci...225..890C | s2cid = 2875906
 }}
</ref> although known oil-shale extraction development projects assert an EROI between 3 and 10.  According to the World Energy Outlook 2010, the EROI of ''ex-situ'' processing is typically 4 to 5 while of ''in-situ'' processing it may be even as low as 2. However, according to the IEA most of used energy can be provided by burning the spent shale or oil-shale gas.<ref name="weo2010 165"/> To increase efficiency when retorting oil shale, researchers have proposed and tested several co-pyrolysis processes.<ref name="co-pyrolisis2">
{{Cite journal
 | title =Fixation of chlorine evolved in pyrolysis of PVC waste by Estonian oil shales
 | last1 = Tiikma | first1=Laine
 | last2 = Johannes | first2=Ille
 | last3 = Luik | first3=Hans
 | journal=Journal of Analytical and Applied Pyrolysis
 | date=March 2006
 | volume=75
 | issue=2
 | pages=205–210
 | doi =10.1016/j.jaap.2005.06.001}}
</ref><ref name="veski1">
{{Cite journal
 | last1 =Veski | first1 =R.
 | last2 =Palu | first2 =V.
 | last3 =Kruusement | first3 =K.
 | title =Co-liquefaction of kukersite oil shale and pine wood in supercritical water
 | journal = [[Oil Shale (journal)|Oil Shale. A Scientific-Technical Journal]]
 | publisher = Estonian Academy Publishers
 | volume =23
 | issue =3
 | pages =236–248
 | year =2006
 | doi =10.3176/oil.2006.3.04
 | s2cid =59478829
 | url=https://www.kirj.ee/public/oilshale/oil-2006-3-4.pdf
 | issn = 0208-189X
 | access-date =16 June 2007}}
</ref><ref name="Morocco">
{{Cite journal
 | last1 = Aboulkas | first1 =A.
 | last2 =El Harfi | first2 =K.
 | last3 =El Bouadili | first3 =A.
 | last4 =Benchanaa | first4 =M.
 | last5 =Mokhlisse | first5 =A.
 | last6 =Outzourit | first6 =A.
 | title = Kinetics of co-pyrolysis of Tarfaya (Morocco) oil shale with high-density polyethylene
 | journal = [[Oil Shale (journal)|Oil Shale. A Scientific-Technical Journal]]
 | publisher = Estonian Academy Publishers
 | volume =24
 | issue =1
 | pages =15–33
 | year =2007
 | doi =10.3176/oil.2007.1.04
 | s2cid =55932225
 | url=https://www.kirj.ee/public/oilshale/oil-2006-3-4.pdf
 | issn = 0208-189X
 | access-date =16 June 2007}}
</ref>

== Environmental considerations ==
{{Main|Environmental impact of the oil shale industry}}

Mining oil shale involves numerous environmental impacts, more pronounced in surface mining than in underground mining.<ref name=mittal>
{{cite web
 | last =Mittal | first =Anu K.
 | title = Unconventional Oil and Gas Production. Opportunities and Challenges of Oil Shale Development
 | publisher = [[Government Accountability Office]]
 | date =10 May 2012
 | url = https://www.gao.gov/assets/600/590761.pdf
 | access-date = 22 December 2012}}
</ref> These include acid drainage induced by the sudden rapid exposure and subsequent oxidation of formerly buried materials; the introduction of metals including [[Mercury (element)|mercury]]<ref>Western Oil Shale Has a High Mercury Content http://www.westernresearch.org/uploadedFiles/Energy_and_Environmental_Technology/Unconventional_Fuels/Oil_Shale/MercuryinOilShale.pdf {{Webarchive|url=https://web.archive.org/web/20110719102244/http://www.westernresearch.org/uploadedFiles/Energy_and_Environmental_Technology/Unconventional_Fuels/Oil_Shale/MercuryinOilShale.pdf |date=19 July 2011 }}</ref> into surface-water and groundwater; increased [[erosion]], sulfur-gas emissions; and air pollution caused by the production of [[Atmospheric particulate matter|particulates]] during processing, transport, and support activities.<ref name="Burnham" /><ref name="openpitimpacts">
{{cite book
 |title= The Abandoned Mine Site Characterization and Cleanup Handbook
 |chapter = Environmental Impacts from Mining
 |chapter-url= https://www.epa.gov/sites/default/files/2015-09/documents/2000_08_pdfs_amscch.pdf
 |pages=3/1–3/11
 |publisher= [[United States Environmental Protection Agency]]
 |date=August 2000
 |access-date=21 June 2010}}
</ref>

Oil-shale extraction can damage the biological and recreational value of land and the ecosystem in the mining area. Combustion and thermal processing generate waste material. In addition, the atmospheric emissions from oil shale processing and combustion include [[carbon dioxide]], a [[greenhouse gas]]. Environmentalists oppose production and usage of oil shale, as it creates even more greenhouse gases than conventional fossil fuels.<ref name="nrdc">
{{cite report
 |title= Driving It Home. Choosing the Right Path for Fueling North America's Transportation Future
 |url= https://www.nrdc.org/sites/default/files/drivingithome.pdf
 |publisher= [[Natural Resources Defense Council]]
 |date= June 2007
 |access-date= 19 April 2008
}}</ref>  Experimental ''in situ'' conversion processes and [[carbon capture and storage]] technologies may reduce some of these concerns in the future, but at the same time they may cause other problems, including [[groundwater pollution]].<ref name="BartisBoston">
{{cite conference
 | url=http://www.aspo-usa.com/fall2006/presentations/pdf/Bartis_J_Boston_2006.pdf
 | conference = World Oil Conference
 | title=Unconventional Liquid Fuels Overview
 | last = Bartis | first = Jim
 | publisher=Association for the Study of Peak Oil & Gas – USA
 | date= 26 October 2006
 | access-date=28 June 2007
 | archive-url = https://web.archive.org/web/20110721161801/http://www.aspo-usa.com/fall2006/presentations/pdf/Bartis_J_Boston_2006.pdf
 | archive-date = 21 July 2011
 | url-status = usurped}}
</ref>  Among the water contaminants commonly associated with oil shale processing are oxygen and nitrogen heterocyclic hydrocarbons. Commonly detected examples include [[quinoline]] derivatives, [[pyridine]], and various alkyl homologues of pyridine, such as [[picoline]] and [[lutidine]].<ref>Sims, G. K. and E.J. O'Loughlin. 1989. Degradation of pyridines in the environment. CRC Critical Reviews in Environmental Control. 19(4): 309–340.</ref>

Water concerns are sensitive issues in arid regions, such as the western U.S. and Israel's [[Negev|Negev Desert]], where plans exist to expand oil-shale extraction despite a water shortage.<ref>{{cite news
 |url          = http://www.deseretnews.com/article/695263708/Oil-shale-rush-is-sparking-concern.html
 |title        = Oil-shale 'rush' is sparking concern
 |last         = Speckman
 |first        = Stephen
 |newspaper    = [[Deseret Morning News]]
 |date         = 22 March 2008
 |access-date  = 6 May 2011
 |archive-date = 16 November 2010
 |archive-url  = https://web.archive.org/web/20101116001214/http://www.deseretnews.com/article/695263708/Oil-shale-rush-is-sparking-concern.html
 |url-status   = dead
}}</ref>  Depending on technology, above-ground retorting uses between one and five barrels of water per barrel of produced shale-oil.<ref name=rand/><ref name=BLM2008/><ref name=water>
{{cite web
 | title = Critics charge energy, water needs of oil shale could harm environment
 | publisher = U.S. Water News Online
 |date=July 2007
 | url = http://www.uswaternews.com/archives/arcsupply/7critchar7.html
 | access-date = 1 April 2008
 | archive-url = https://web.archive.org/web/20080618074850/http://www.uswaternews.com/archives/arcsupply/7critchar7.html
 | archive-date = 18 June 2008}}
</ref><ref name=Al-Ayed>
{{cite web
 | title = Jordan Oil Shale Project
 | last = Al-Ayed | first = Omar
 | publisher = [[Al-Balqa` Applied University]]
 | year = 2008
 | url = http://www.jordanoilshale.net/page4.aspx
 | access-date = 15 August 2008
 | url-status = usurped
 | archive-url = https://web.archive.org/web/20080603231353/http://www.jordanoilshale.net/page4.aspx
 | archive-date = 3 June 2008}}
</ref> A 2008 programmatic [[environmental impact statement]] issued by the U.S. [[Bureau of Land Management]] stated that surface mining and retort operations produce {{convert|2|to|10|USgal|sp=us}} of waste water per {{convert|1|ST|sp=us}} of processed oil shale.<ref name=BLM2008>{{cite book
 |chapter-url          = http://ostseis.anl.gov/documents/fpeis/vol1/OSTS_FPEIS_Vol1_Ch4.pdf
 |title        = Proposed Oil Shale and Tar Sands Resource Management Plan Amendments to Address Land Use Allocations in Colorado, Utah, and Wyoming and Final Programmatic Environmental Impact Statement
 |chapter      = Chapter 4. Effects of Oil Shale Technologies
 |pages        = 4‑3
 |publisher    = [[Bureau of Land Management]]
 |date         = September 2008
 |access-date   = 7 August 2010
 |id           = FES 08-32
 |archive-url  = https://web.archive.org/web/20100527214525/http://ostseis.anl.gov/documents/fpeis/vol1/OSTS_FPEIS_Vol1_Ch4.pdf
 |archive-date = 27 May 2010
 |url-status     = dead
 |df           = dmy-all
}}</ref> ''In situ'' processing, according to one estimate, uses about one-tenth as much water.<ref>
{{cite journal
 | title=Hopes for shale oil are revived
 | last = Fischer | first = Perry A.
 | url=http://www.worldoil.com/magazine/MAGAZINE_DETAIL.asp?ART_ID=2658&MONTH_YEAR=Aug-2005
 | journal = World Oil Magazine
 | publisher= [[Gulf Publishing Company]]
 |date=August 2005
 | archive-url = https://web.archive.org/web/20061109140826/http://worldoil.com/magazine/MAGAZINE_DETAIL.asp?ART_ID=2658&MONTH_YEAR=Aug-2005
 | archive-date = 9 November 2006
 | access-date=1 April 2008}}
</ref>

[[environmentalism|Environmental]] activists, including members of [[Greenpeace]], have organized strong protests against the oil shale industry. In one result, [[Queensland Energy Resources]] put the proposed [[Stuart Oil Shale Project]] in Australia on hold in 2004.<ref name="Burnham" /><ref>
{{cite web
 | url=https://www.abc.net.au/news/2004-07-22/greenpeace-happy-with-part-closure-of-shale-oil/2013172
 | title=Greenpeace happy with part closure of shale oil plant
 | publisher=[[Australian Broadcasting Corporation]]
 | date=22 July 2004
 | access-date=19 May 2008
}}</ref>

== Extraterrestrial oil shale ==
Some comets contain massive amounts of an organic material almost identical to high grade oil shale, the equivalent of cubic kilometers of such mixed with other material;<ref name = IdahoNationalLab>Dr. A. Zuppero, U.S. Department of Energy, Idaho National Engineering Laboratory. [http://www.neofuel.com/zuppero-1995-water-ice-nearly-everywhere-114647.pdf Discovery Of Water Ice Nearly Everywhere In The Solar System]</ref> for instance, corresponding hydrocarbons were detected in a probe fly-by through the tail of [[Halley's Comet]] in 1986.<ref name="Huebner1990">{{cite book
| editor1-last = Huebner | editor1-first = Walter F.
| year=1990
| title=Physics and Chemistry of Comets
| publisher=Springer-Verlag
| isbn=978-3-642-74805-9}}
</ref>

== See also ==
{{Portal|Energy|Earth sciences}}
* [[Caprock]]
* {{annotated link|Core Research Center}} – a United States Geological Survey facility dedicated to preserving valuable rock-samples threatened with disposal or destruction – including oil shales
* [[Creveney shale mining operation]]
* {{annotated link|Kukersite}} – a well-analyzed marine oil shale found in the Baltic Sea basin
* [[Les Télots Mine]]
* {{annotated link|Mitigation of peak oil}} – discussion of attempts to delay and minimize the impact of "[[peak oil]]" (the point in time of maximum global petroleum production), including the development of unconventional oil resources
* {{annotated link|Oil reserves}} – discussion of global crude-oil supplies
* {{annotated link|Oil sands}}
* [[Spent shale]]
* {{annotated link|Tasmanite}} – a marine oil shale found in Tasmania
* {{annotated link|Torbanite}} – a lacustrine oil shale found in Scotland
* {{annotated link|World energy consumption}}

==References==
{{Reflist|30em}}

== Bibliography ==
{{Anchor|Books|Bibliography}}
{{refbegin}}
* {{Cite book  | editor1-last = Teh Fu Yen | editor2-last = Chilingar | editor2-first = George V. | last = Cane | first= R.F. | title = Oil Shale | chapter= The origin and formation of oil shale | publisher = Elsevier | location = Amsterdam | pages = 1–12; 56 | year = 1976 | chapter-url = https://books.google.com/books?id=qkU7OcVkwaIC&pg=PA56 | isbn = 978-0-444-41408-3 | ref=yen}}
* {{cite book | title = Survey of energy resources | chapter = Oil Shale | last = Dyni | first = John R. | editor1-last = Clarke | editor1-first = Alan W. | editor2-last = Trinnaman | editor2-first = Judy A. | publisher = [[World Energy Council]] | year = 2010 | edition = 22 | url = https://www.worldenergy.org/wp-content/uploads/2012/09/ser_2010_report_1.pdf | isbn = 978-0-946121-02-1 | ref = wec | url-status = live | archive-url = https://web.archive.org/web/20120304064924/http://www.worldenergy.org/documents/ser_2010_report.pdf | archive-date = 4 March 2012 | df = dmy-all }}
* {{cite book | url = https://www.worldenergy.org/assets/images/imported/2013/09/Complete_WER_2013_Survey.pdf | title = World Energy Resources 2013 Survey | chapter = Unconventional oil | year = 2013 | work = [[World Energy Council]] | page = 2.46 | isbn = 9780946121298 | archive-url = https://web.archive.org/web/20140221160815/http://www.worldenergy.org/wp-content/uploads/2013/09/Complete_WER_2013_Survey.pdf | archive-date = 2014-02-21 | url-status = live | ref = 2013 }}
* {{cite book | title = Annual Energy Outlook 2006 | publisher = [[Energy Information Administration]] | date=February 2006 | url = https://www.eia.gov/outlooks/archive/aeo06/pdf/0383(2006).pdf | ref = aeo2006}}
* {{Cite book | title= World Energy Outlook 2010 | work = [[International Energy Agency|IEA]] | publisher = [[OECD]] | location = [[Paris]] | year = 2010 | isbn = 978-92-64-08624-1| ref=weo2010}}
* {{cite book | title= World Energy Outlook 2013 | year = 2013 | work = [[International Energy Agency|IEA]] | publisher = [[OECD]] | isbn=978-92-64-20130-9 | ref = 2013}}
* {{Cite book | last = Lee | first = Sunggyu | title = Oil Shale Technology | publisher = CRC Press | year = 1991 | url = https://books.google.com/books?id=N0wMCusO6yIC&pg=PA10 | isbn = 978-0-8493-4615-6 | ref=lee}}
* {{Cite book | last = Mushrush | first = George | title = Petroleum Products: Instability And Incompatibility | series = Applied energy technology | publisher = [[CRC Press]] | year = 1995 | url = https://books.google.com/books?id=kTClrgGyc5oC&pg=PA39 | isbn = 9781560322979 | ref = mushrush}}
* {{Cite book | last = van Krevelen | first = Dirk Willem | title = Coal--typology, physics, chemistry, constitution | publisher = [[Elsevier]] | series = Coal Science and Technology Series | edition = 3 | year = 1993 | isbn = 978-0-444-89586-8 | ref=vankrevelen}}
* {{Cite book | title = World energy resources. Oil 2016 | publisher = [[World Energy Council]] | year = 2016 | url = https://www.worldenergy.org/wp-content/uploads/2016/10/World-Energy-Resources-Full-report-2016.10.03.pdf | isbn =  978-0-946121-62-5 | ref=wec2016}}
{{refend}}

== External links ==
{{Spoken Wikipedia|Oil_shale.ogg|date=2008-05-26}}
{{Stack|{{Commons category|Oil shale}}{{NIE Poster|Bituminous Shales|year=1905}}}}
* {{cite journal| url=https://www.kirj.ee/oilshale/
|title=Oil Shale. A Scientific-Technical Journal |journal=Bulletin des Sciences |publisher= Estonian Academy Publishers|issn=0208-189X |access-date=22 April 2008 }}

{{Petroleum industry|state=expanded}}
{{Rock type}}
{{Portal bar|Earth sciences|Energy|Technology|Engineering}}
{{Authority control}}

{{DEFAULTSORT:Oil Shale}}
[[Category:Oil shale| ]]
[[Category:Sedimentary rocks]]