Editing Oil shale (section)

== 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=http://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= http://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 = http://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>