Oil Shale
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Oil_Shale".

Combustion of oil shale
Combustion of oil shale

Oil shale is a fine-grained sedimentary rock, containing significant amounts of kerogen (a solid mixture of organic chemical compounds), from which liquid hydrocarbons can be manufactured. The name oil shale has been described as a promotional misnomer, since the rock is not necessarily a shale and its kerogen is not crude oil; it requires more processing than crude oil, which affects its economic viability as a crude oil substitute.[1][2] Deposits of oil shale are located around the world, including major deposits in the United States. Global deposits are estimated as equivalent to 2.8 trillion to 3.3 trillion barrels (450×109 to 520×109 m3) of recoverable oil.[2][3][4][5]

The kerogen in oil shale can be converted to synthetic crude oil through the chemical process of pyrolysis. When heated to a sufficiently high temperature a vapor is driven off which can be distilled (retorted) to yield a petroleum-like shale oil—a form of non-conventional oil—and combustible shale gas (shale gas can also refer to gas occurring naturally in shales). Oil shale can also be burnt directly as a low-grade fuel for power generation and heating purposes, and can be used as a raw material in the chemical and construction materials industries.[6][2]

Oil shale has gained attention as an energy resource as the price of conventional sources of petroleum has risen, and as a way to secure independence from external suppliers of energy.[7][8] The oil shale industry is well-established in Estonia, China, and Brazil, and the United States is taking steps in that direction. At the same time oil shale mining and processing involves a number of environmental issues, such as land use, waste disposal, water use and waste water management, and air pollution.[9][10] The industry has foundered in Australia due to its opposition on these grounds.

content

Contents

Geology

Main article: Oil shale geology
Outcrop of Ordovician oil shale (kukersite), northern Estonia
Outcrop of Ordovician oil shale (kukersite), northern Estonia

Oil shale is an organic-rich sedimentary rock, which belongs to the group of sapropel fuels.[11] It is differentiated from bitumen-impregnated rocks (tar sands and petroleum reservoir rocks), humic coals and carbonaceous shale. While tar sands have been created by biodegradation of oil, the kerogen in oil shales has not yet been naturally transformed into petroleum by heat and pressure.[2][12][13] Coal contains a higher percentage of organic matter than oil shale. In commercial grades of oil shale the ratio of organic matter to mineral matter is about 0.75:5 to 1.5:5. At the same time, the organic matter in oil shale has an atomic ratio of hydrogen to carbon approximately the same as for crude oil and four to five times higher than for coals.[2][11]

Oil shale does not have a definite geological definition nor a specific chemical formula. Oil shales vary considerably in their mineral content, chemical composition, age, type of kerogen, and depositional history.[14] Its organic components are derived from a variety of organisms, such as the remains of algae, spores, pollen, plant cuticles and corky fragments of herbaceous and woody plants, and cellular debris from other aquatic and land plants.[2][15] Some deposits contain significant fossils; Germany's Messel Pit is a Unesco World Heritage Site. The mineral matter in oil shale includes various fine-grained silicates and carbonates.[11][6]

Based on their composition, oil shales are classified as carbonate-rich shales, siliceous shales, and cannel shales.[16] Another classification, assigning kerogen types, is based on the hydrogen, carbon, and oxygen content of oil shales' original organic matter. This classification is known as the van Krevelen diagram.[14] The most used classification of oil shales was developed between 1987 and 1991 by Adrian C. Hutton of the University of Wollongong, adapting petrographic terms from coal terminology. According to this classification, oil shales are designated as terrestrial, lacustrine (lake-bottom-deposited), or marine (ocean bottom-deposited), based on the environment where the initial biomass was deposited. [6][17] Hutton's classification scheme has proven useful in estimating the yield and composition of the extracted oil.[2]

Reserves

Main article: Oil shale reserves
Fossils in Ordovician oil shale (kukersite), northern Estonia
Fossils in Ordovician oil shale (kukersite), northern Estonia

Some analysts, along with the United States Geological Survey, draw a distinction between oil shale resources and oil shale reserves. "Resources" may refer to all oil shale deposits, while "reserves" is more narrowly defined as those deposits from which oil can profitably be extracted using existing technologies. Since extraction technologies are still developing, the amount of recoverable kerogen can only be estimated.[6][18] Although oil shale resources occur in many countries, only 33 countries possess deposits of possible economic value.[19][20] Well-explored deposits, which could be classified as reserves, include the 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, and Russia. It is expected that these deposits would yield at least 40 liters of shale oil per tonne of shale, using the Fischer assay.[6][14]

Total world resources of oil shale were estimated in 2005 at 411 gigatons, which is enough to yield 2.8 to 3.3 trillion barrels of shale oil.[2][3][4][5] This is more than world's proven conventional oil reserves, estimated to be 1.317 trillion barrels (209.4×109 m3), as of 1 January 2007.[21] The largest deposits in the world are found in the United States in the Green River basin, which covers portions of Colorado, Utah, and Wyoming; about 70% of this resource is located on federally owned or managed land.[22] Deposits in the United States constitute 62% of world resources; together, the United States, Russia and Brazil account for 86% of the world's resources in terms of shale oil content.[19] These figures are considered tentative, as several deposits have not yet been explored or analyzed.[6][2]

History

Main article: History of the oil shale industry
Production of oil shale (megatons) in Estonia (Estonia deposit), Russia (Leningrad and Kashpir deposits), United Kingdom (Scotland, Lothians), Brazil (Iratí Formation), China (Maoming and Fushun deposits), and Germany (Dotternhausen) from 1880 to 2000
Production of oil shale (megatons) in Estonia (Estonia deposit), Russia (Leningrad and Kashpir deposits), United Kingdom (Scotland, Lothians), Brazil (Iratí Formation), China (Maoming and Fushun deposits), and Germany (Dotternhausen) from 1880 to 2000[6]

Oil shale has been used as a fuel since prehistoric times, since it generally burns without any processing.[23] It was polished and formed into ornaments by Iron Age Britons.[24] Modern industrial oil shale mining began in 1837 in Autun, France, followed by Scotland, Germany, and several other countries.[2][25] Operations during the 19th century focused on the production of kerosene, lamp oil, and paraffin; these products helped supply the growing demand for lighting that arose during the Industrial Revolution.[26] Fuel oil, lubricating oil and grease, and ammonium sulfate were also produced.[27] The oil shale industry expanded immediately before World War I because of limited access to conventional petroleum resources and the mass production of automobiles and trucks, which generated an increase in gasoline consumption.

Although the Estonian and Chinese oil shale industries continued to grow after World War II, most other countries abandoned their projects due to high processing costs and the availability of cheaper petroleum.[6][2][25][28] Following the 1973 oil crisis, world production of oil shale reached a peak of 46 million tonnes in 1980 before falling to about 16 million tonnes in 2000, due to competition from cheap conventional petroleum.[19][9] On 2 May 1982, known as "Black Sunday", Exxon canceled its US$5 billion Colony Shale Oil Project near Parachute, Colorado laying off more than 2,000 workers, and leaving a trail of home foreclosures and small-business bankruptcies.[29] It led the United States Congress to abolish its Synthetic Liquid Fuels Program.[30]

The global oil shale industry began to revive in the mid-1990s. In 2003, an oil shale development program was restarted in the United States. A commercial leasing program permitting the extraction of oil shale and tar sand resources on federal lands was introduced in 2005, in accordance with the Energy Policy Act of 2005.[31][32][33]

Industry

Main article: Oil shale industry

As of 2008, oil shale is used industrially in Brazil, China, Estonia and to some extent in Germany, Israel, and Russia. Several additional countries were assessing their reserves or had built experimental production plants, while others had phased out their oil shale industry.[2] Oil shale is used for oil production in Estonia, Brazil, and China; for power generation in Estonia, China, Israel, and Germany; for cement production in Estonia, Germany, and China; and by chemical industries in China, Estonia, and Russia.[28][2][34][35] As of 2005, Estonia alone accounted for about 70% of the world's oil shale production.[34][36]

Romania and Russia have run oil shale-fired power plants, but have shut them down or switched to other fuel sources such as natural gas. Jordan and Egypt are planning to construct oil shale-fired power plants, while Canada and Turkey plan to burn oil shale along with coal for power generation.[2][19][37] Oil shale is used as the main fuel for power generation only in Estonia, where the oil shale-fired Narva Power Plants accounted for 95% of electrical generation in 2005.[38]

Extraction and processing

Main article: Oil shale extraction
Shell's experimental in-situ oil shale facility, Piceance Basin, Colorado
Shell's experimental in-situ oil shale facility, Piceance Basin, Colorado

Oil shale is usually mined and then shipped elsewhere, after which it is directly burnt to generate electricity or undergoes further processing. The most-often used methods of surface mining are open pit mining and strip mining. These procedures remove most of the overlying material to expose the oil shale deposits, and are practical when the deposits are close to the surface. Underground mining of oil shale, which removes less of the overlying material, employs the room-and-pillar method.[39]

The extraction of its useful components usually takes place above ground (ex situ processing), although several newer technologies perform this underground (on-site or in situ processing).[40] In either case, after access to the shale is gained, its kerogen is converted to synthetic crude oil and shale gas through the chemical process of pyrolysis. Most conversion technologies involve heating shale in the absence of oxygen to a temperature at which kerogen is decomposed (pyrolysed) into gas, condensable oil, and a solid residue; this usually takes place between 450 °C (842 °F) and 500 °C (932 °F).[18] The process of decomposition begins at relatively low temperatures (300 °C/570 °F), but proceeds more rapidly and more completely at higher temperatures.[41]

During the course of in-situ processing, the oil shale is heated underground. These 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.[42] Several companies have patented methods for in-situ retorting. However, most of these methods are still in the experimental phase. The methods are usually classified as true in-situ processes (TIS) and modified in-situ processes (MIS). True in-situ processes do not involve mining the oil shale. Modified in-situ processes drill a large shaft to transport workers and equipment to the shale formation, fracture the deposit and crush it, and ignite the rubble.[43]

There are hundreds of patents for oil shale retorting technologies;[44] however, only a few dozen have been tested. As of 2006, only four technologies were in commercial use: Kiviter, Galoter, Fushun, and Petrosix.[45]

Applications and products

Oil shale can be used as a fuel for thermal power plants, where, like coal, it is burned to drive steam turbines; some of these plants employ the resulting heat for district heating of homes and businesses. Sizable oil shale-fired power plants are located in Estonia, which has an installed capacity of 2,967 megawatts (MW), Israel (12.5 MW), China (12 MW), and Germany (9.9 MW).[19][46]

In addition to its use as a fuel, oil shale may also be used for production of specialty carbon fibers, adsorbent carbons, carbon black, phenols, resins, glues, tanning agents, mastic, road bitumen, cement, bricks, construction and decorative blocks, soil additives, fertilizers, rock wool insulation, glass, and pharmaceutical products.[34] However, oil shale use for production of these items is still small or only in its experimental stages.[6][2] Some oil shales yield sulfur, ammonia, alumina, soda ash, uranium, and nahcolite as shale oil extraction byproducts. Between 1946 and 1952, a marine type of Dictyonema shale was used for uranium production in Sillamäe, Estonia, and between 1950 and 1989 alum shale was used in Sweden for the same purposes.[6] Another of its uses has been as a substitute for natural gas, but as of 2008, producing shale gas as a natural gas substitute is not economically feasible.[47][48]

The oil derived from oil shale is not a direct substitute for crude oil in all applications. It contains higher concentrations of olefins, oxygen, and nitrogen than conventional crude oil, as well as higher viscosities. By comparison with West Texas Intermediate, the benchmark standard for crude oil in the futures contract market, shale oil sulfur content ranges up to 9.5% by weight, where West Texas Intermediate's sulfur content is limited to no more than 0.42%.[49][50] The higher concentrations of these materials means that the oil must undergo considerable upgrading before being used as oil refinery feedstock.[51] Shale oil does not contain the full range of hydrocarbons used in modern gasoline production, and could only be used to produce middle-distillates such as kerosene, jet fuel, and diesel fuel.[4] Worldwide demand for these middle distillates, however, is increasing rapidly.[52]

Economics

Main article: Oil shale economics
Medium-term prices for light-sweet crude oil in US dollars, 2005–2007 (not adjusted for inflation)
Medium-term prices for light-sweet crude oil in US dollars, 2005–2007 (not adjusted for inflation)

During the beginning of the 20th century, the crude oil industry expanded. Since then, the various attempts to develop oil shale deposits have been successful only when the cost of shale oil production in a given region was less than the price of crude oil or its other substitutes.[53] According to a 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, upgrading plant, supporting utilities, and spent shale reclamation), would be between US$70–95 ($440–600/m3, adjusted to 2005 values). This estimate considers varying levels of kerogen quality and extraction efficiency. In order for the operation to be profitable, the price of crude oil would need to remain above these levels. The analysis also discusses the expectation that processing costs would drop after the complex was established. The hypothetical unit would see a cost reduction of 35–70% after its first 500 million barrels (79×106 m3) were produced. Assuming an increase in output of 25 thousand barrels per day (4.0×103 m3/d) during each year after the start of commercial production, the costs would then be expected to decline to $35–48 per barrel ($220–300/m3) within 12 years. After achieving the milestone of 1 billion barrels (160×106 m3), its costs would decline further to $30–40 per barrel ($190–250/m3).[39][34] A comparison of the proposed US oil shale industry to the Alberta tar sands industry has been drawn (the latter enterprise generated over one million barrels of oil per day in late 2007), stating that "the first-generation facility is the hardest, both technically and economically".[54][55]

Royal Dutch Shell has announced that its in situ extraction technology in Colorado could be competitive at prices over $30 per barrel ($190/m3), while other technologies at full-scale production assert profitability at oil prices even lower than $20 per barrel ($130/m3).[56][57][58][43] To increase the efficiency of oil shale retorting, several co-pyrolysis processes have been proposed and tested.[59][60][61][62][63]

Shale oil production has been unfavorably compared to other unconventional oil technologies. It is argued that liquefaction of coal is less expensive than oil shale extraction, as well as producing more oil with fewer environmental impacts.[64] In 1972, the journal Petrole Informations (ISSN 0755-561X) noted that one ton of coal yielded 650 liters of oil while one ton of oil shale yielded only 150 liters of shale oil.[25]

A critical measure of the viability of oil shale as an energy source is the ratio of the energy produced by the shale to the energy used in its mining and processing, a ratio known as "Energy Returned on Energy Invested" (EROEI). A 1984 study estimated the EROEI of the various known oil shale deposits as varying between 0.7–13.3.[65] Royal Dutch Shell has reported an EROEI of three to four on its in situ development, Mahogany Research Project.[56][66][67] An additional economic consideration is the water needed in the oil shale retorting process, which may pose a problem in areas with water scarcity.

Environmental considerations

Main article: Environmental impact of oil shale industry

Oil shale mining involves a number of environmental impacts, more pronounced in surface mining than in underground mining. They include acid drainage induced by the sudden rapid exposure and subsequent oxidation of formerly buried materials, the introduction of metals into surface water and groundwater, increased erosion, sulfur-gas emissions, and air pollution caused by the creation of particulates during processing, transport, and support activities.[9][10] In 2002, about 97% of air pollution, 86% of total waste and 23% of water pollution in Estonia came from the power industry, which uses oil shale as the main resource for its power production.[68]

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 major greenhouse gas. Environmentalists oppose production and usage of oil shale, as it creates even more greenhouse gases than conventional fossil fuels.[69] 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.[70]

Concerns have been expressed over the oil shale industry's use of water. In 2002, 91% of the water consumed in Estonia was used in the oil shale-fired power industry.[68] Depending on technology, above-ground retorting uses between one and five barrels of water per barrel of produced shale oil.[39][71][72][73] A 2007 programmatic environmental impact statement issued by the US Bureau of Land Management stated that surface mining and retort operations produce two to ten US gallons (8–38 l) of wastewater per tonne of processed oil shale.[71] In situ processing, according to one estimate, uses about one-tenth as much water.[74] Water concerns are particularly sensitive issue in arid regions, such as the western US and Israel's Negev Desert, where there are plans to expand the oil shale industry despite a water shortage.[75][76]

Environmental activists, including Greenpeace, have organized strong protests against the industry. As a result, the proposed Stuart Oil Shale Project in Australia was put on hold in 2004.[9][77][78]

See also

Energy Portal

Footnotes

  1. ^ Shale Oil: The Elusive Energy (PDF). Colorado School of Mines. Retrieved on 2008-03-20.
  2. ^ a b c d e f g h i j k l m n o (2007) Survey of energy resources (PDF), edition 21, World Energy Council (WEC), 93–115. ISBN 0946121265. Retrieved on 2007-11-13. 
  3. ^ a b (February 2006). "Annual Energy Outlook 2006" (PDF). Energy Information Administration. Retrieved on 2008-04-18.
  4. ^ a b c Andrews, Anthony (2006-04-13). "Oil Shale: History, Incentives, and Policy" (PDF). Congressional Research Service. Retrieved on 2007-06-25.
  5. ^ a b (April 2006). "NPR's National Strategic Unconventional Resource Model" (PDF). United States Department of Energy. Retrieved on 2007-07-09.
  6. ^ a b c d e f g h i j Dyni, John R.. "Geology and resources of some world oil-shale deposits. Scientific Investigations Report 2005–5294" (PDF). U.S. Department of the Interior. U.S. Geological Survey. Retrieved on 2007-07-09.
  7. ^ (September 2006). "Energy Security of Estonia" (PDF). Estonian Foreign Policy Institute. Retrieved on 2007-10-20.
  8. ^ Oil Shale Activities. United States Department of Energy. Retrieved on 2007-10-20.
  9. ^ a b c d Burnham, A. K. (2003-08-20). "Slow Radio-Frequency Processing of Large Oil Shale Volumes to Produce Petroleum-like Shale Oil" (PDF). Lawrence Livermore National Laboratory. UCRL-ID-155045 Retrieved on 2007-06-28.
  10. ^ a b (2006-08-02). "Environmental Impacts from Mining" (PDF). US Office of Surface Mining Reclamation and Enforcement. Retrieved on 2008-03-29.
  11. ^ a b c Ots, Arvo (2007-02-12). "Estonian oil shale properties and utilization in power plants" (PDF). Energetika 53 (2): 8–18. Lithuanian Academy of Sciences Publishers. Retrieved on 2007-11-07. 
  12. ^ Nield, Ted (2007-02-17). Shale of the Century. Geological Society of London. Retrieved on 2007-10-20.
  13. ^ O’Neil, William D. (2001-06-11). "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." (PDF). 94–95CNA Corporation. Retrieved on 2008-04-19.
  14. ^ a b c Altun, N. E. (2006). "Oil Shales in the world and Turkey; reserves, current situation and future prospects: a review" (PDF). Oil Shale. A Scientific-Technical Journal 23 (3): 211–227. Estonian Academy Publishers. ISSN 0208-189X. Retrieved on 2007-06-16. 
  15. ^ Alali, Jamal (2006-11-07). "Jordan Oil Shale, Availability, Distribution, And Investment Opportunity" (PDF). Retrieved on 2008-03-04. 
  16. ^ Lee, Sunggyu (1991). Oil Shale Technology. CRC Press, 10. ISBN 0849346150. Retrieved on 2007-07-09. 
  17. ^ Hutton, A.C. (1987). "Petrographic classification of oil shales". International Journal of Coal Geology 8: 203–231. Elsevier Science. ISSN 0166-5162. 
  18. ^ a b Youngquist, Walter (1998). "Shale Oil - The Elusive Energy" (PDF). Hubbert Center Newsletter (4). Colorado School of Mines. Retrieved on 2008-04-17. 
  19. ^ a b c d e Brendow, K. (2003). "Global oil shale issues and perspectives. Synthesis of the Symposium on Oil Shale. 18–19 November, Tallinn" (PDF). Oil Shale. A Scientific-Technical Journal 20 (1): 81–92. Estonian Academy Publishers. ISSN 0208-189X. Retrieved on 2007-07-21. 
  20. ^ Qian, Jialin (2003). "Oil Shale Development in China" (PDF). Oil Shale. A Scientific-Technical Journal 20 (3): 356–359. Estonian Academy Publishers. ISSN 0208-189X. Retrieved on 2007-06-16. 
  21. ^ Chapter 3 - Petroleum and Other Liquids Fuels. International Energy Outlook 2007. Energy Information Administration (May 2007). Retrieved on 2008-04-20.
  22. ^ About Oil Shale. Argonne National Laboratory. Retrieved on 2007-10-20.
  23. ^ Bibliographic Citation: Non-synfuel uses of oil shale. U.S. Department of Energy. Retrieved on 2008-03-20.
  24. ^ Ian West (2008-01-06). Kimmeridge - The Blackstone - Oil Shale. University of Southampton. Retrieved on 2008-04-21.
  25. ^ a b c Laherrère, Jean (2005). "Review on oil shale data" (PDF). Hubbert Peak. Retrieved on 2007-06-17.
  26. ^ Doscher, Todd M.. Petroleum. MSN Encarta. Retrieved on 2008-04-22.
  27. ^ Oil Shale. American Association of Petroleum Geologists. Retrieved on 2008-03-31.
  28. ^ a b Yin, Liang (2006-11-07). "Current status of oil shale industry in Fushun, China" (PDF). Retrieved on 2007-06-29.
  29. ^ Collier, Robert. "Coaxing oil from huge U.S. shale deposits", San Fransisco Chronicle, 2006-09-04. Retrieved on 2008-05-14. 
  30. ^ Manski, Rebecca. "Scrapping the Oil Shale Scam, Investing in Infinite Energy", BUSTAN: Environmental Justice in Israel’s Negev, 2006-09-02. Retrieved on 2008-05-14. 
  31. ^ Bureau of Land Management (2005-09-20). "Nominations for Oil Shale Research Leases Demonstrate Significant Interest in Advancing Energy Technology.". Press release. Retrieved on 2007-07-10.
  32. ^ Bureau of Land Management (2006-08-25). "BLM Publishes Advance Notice of Proposed Rulemaking on Commercial Oil Shale Leasing.". Press release. Retrieved on 2008-04-05.
  33. ^ What's in the Oil Shale and Tar Sands Leasing Programmatic EIS. Oil Shale and Tar Sands Leasing Programmatic EIS Information Center. Retrieved on 2007-07-10.
  34. ^ a b c d "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" (PDF) (May 2007). European Academies Science Advisory Council. Retrieved on 2007-11-25. 
  35. ^ Alali, Jamal (2006). "Oil Shale in Jordan" (PDF). Natural Resources Authority of Jordan. Retrieved on 2007-06-29.
  36. ^ (2005). "Non-Nuclear Energy Research in Europe – A comparative study. Country Reports A – I. Volume 2" (PDF). European Commission. Directorate-General for Research. EUR 21614/2 Retrieved on 2007-06-29.
  37. ^ Hamarneh, Yousef; Alali, Jamal; Sawaged, Suzan (1998; 2006). "Oil Shale Resources Development In Jordan" (PDF). Amman: Natural Resources Authority of Jordan. Retrieved on 2007-06-16. 
  38. ^ (2006). "Estonian Energy in Figures 2005" (PDF). Ministry of Economic Affairs and Communications. Retrieved on 2007-10-22.
  39. ^ a b c Bartis, James T. (2005). "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" (PDF). The RAND Corporation. Retrieved on 2007-06-29.
  40. ^ Burnham, Alan K. (2006-10-16). "Comparison of the Acceptability of Various Oil Shale Processes" (PDF). 26th Oil Shale Symposium. UCRL-CONF-226717 Retrieved on 2007-06-23.
  41. ^ Koel, Mihkel (1999). "Estonian oil shale". Oil Shale. A Scientific-Technical Journal (Extra). Estonian Academy Publishers. ISSN 0208-189X. Retrieved on 2007-07-21. 
  42. ^ Ennis, D.L. (2006-08-15). "Oil Shale—An Investment We Can’t Afford". California Chronicle. Retrieved on 2007-07-26.
  43. ^ a b (2004). "Strategic Significance of America’s Oil Shale Resource. Volume II Oil Shale Resources, Technology and Economics" (PDF). United States Department of Energy. Retrieved on 2007-06-23.
  44. ^ Process for the recovery of hydrocarbons from oil shale. FreePatentsOnline. Retrieved on 2007-11-03.
  45. ^ Qian, Jialin (2006-11-07). "World oil shale retorting technologies" (PDF). Retrieved on 2007-06-29.
  46. ^ Qian, Jialin. "One Year’s Progress in the Chinese Oil Shale Business" (PDF). China University of Petroleum. Retrieved on 2007-10-06.
  47. ^ Schora, F. C.; Tarman, P. B.; Feldkirchner, H. L. & Weil, S. A. (1976), "Hydrocarbon fuels from oil shale", Proceedings (American Institute of Chemical Engineers) 1: 325–330, A77-12662 02-44 
  48. ^ Valgma, Ingo. Map of oil shale mining history in Estonia. Mining Institute of Tallinn Technical University. Retrieved on 2007-07-21.
  49. ^ Dyni (1983-04-01). "Distribution and origin of sulfur in Colorado oil shale". 16th Oil Shale Symposium Proceedings: 144–159. U.S. Geological Survey. CONF-830434-. Retrieved on 2007-10-22. 
  50. ^ Al-Harahsheh, Adnan (2003-10-16). "Sulfur distribution in the oil fractions obtained by thermal cracking of Jordanian El-Lajjun oil Shale". Energy. Elsevier. Retrieved on 2007-10-22. 
  51. ^ Lee, Sunggyu (1991). Oil Shale Technology. CRC Press, 6. ISBN 0849346150. Retrieved on 2007-07-09. 
  52. ^ Statement Of Daniel Yergin, Chairman of Cambridge Energy Research Associates, Before The Committee On Energy And Commerce/U.S. House Of Representatives. United States House of Representatives (2006-05-04). Retrieved on 2008-04-20.
  53. ^ Rapier, Robert (2006-06-12). "Oil Shale Development Imminent". R-Squared Energy Blog. Retrieved on 2007-06-22.
  54. ^ A Reporter at Large:Unconventional Crude. The New Yorker (2007-11-12). Retrieved on 2008-03-31.
  55. ^ Is Oil Shale The Answer To America's Peak-Oil Challenge? (PDF). US Department of Energy (2008-02-08). Retrieved on 2008-03-31.
  56. ^ a b Seebach, Linda (2005-09-02). Shell's ingenious approach to oil shale is pretty slick. Rocky Mountain News. Retrieved on 2007-06-02.
  57. ^ Schmidt, S. J. (2003). "New directions for shale oil:path to a secure new oil supply well into this century: on the example of Australia" (PDF). Oil Shale. A Scientific-Technical Journal 20 (3): 333–346. Estonian Academy Publishers. ISSN 0208-189X. Retrieved on 2007-06-02. 
  58. ^ Krauss, Leah (2006-11-07). Analysis: Israel sees shale replacing oil. United Press International. Retrieved on 2007-07-29.
  59. ^ Tiikma, Laine (2002). "Co-pyrolysis of waste plastics with oil shale". Proceedings. Symposium on Oil Shale 2002, Tallinn, Estonia: 76. 
  60. ^ Tiikma, Laine (March 2006). "Fixation of chlorine evolved in pyrolysis of PVC waste by Estonian oil shales" (PDF). Journal of Analytical and Applied Pyrolysis 75 (2): 205–210. Retrieved on 2007-10-20. 
  61. ^ Veski, R. (2006). "Co-liquefaction of kukersite oil shale and pine wood in supercritical water" (PDF). Oil Shale. A Scientific-Technical Journal 23 (3): 236–248. Estonian Academy Publishers. ISSN 0208-189X. Retrieved on 2007-06-16. 
  62. ^ Aboulkas, A. (2007). "Kinetics of co-pyrolysis of Tarfaya (Morocco) oil shale with high-density polyethylene" (PDF). Oil Shale. A Scientific-Technical Journal 24 (1): 15–33. Estonian Academy Publishers. ISSN 0208-189X. Retrieved on 2007-06-16. 
  63. ^ Ozdemir, M. (2006-11-07). "Copyrolysis of Goynuk oil shale and thermoplastics" (PDF). Retrieved on 2007-06-29.
  64. ^ (2006). "Backgrounder: Negev Oil Shale" (PDF). BUSTAN: Environmental Justice in Israel’s Negev. Retrieved on 2008-05-14.
  65. ^ Cleveland, Cutler J. (1984-08-31). "Energy and the U.S. Economy: A Biophysical Perspective" (PDF). Science 225 (4665): 890–897. American Association for the Advancement of Science. ISSN 00368075. Retrieved on 2007-08-28. 
  66. ^ (2006-02-15). "Oil Shale Test Project. Oil Shale Research and Development Project" (PDF). Shell Frontier Oil and Gas. Retrieved on 2007-06-30.
  67. ^ Reiss, Spencer (2005-12-13). Tapping the Rock Field. WIRED Magazine. Retrieved on 2007-08-27.
  68. ^ a b Raukas, Anto (2004). "Opening a new decade" (PDF). Oil Shale. A Scientific-Technical Journal 21 (1): 1–2. Estonian Academy Publishers. ISSN 0208-189X. Retrieved on 2008-05-14. 
  69. ^ (June 2007). "Driving It Home. Choosing the Right Path for Fueling North America's Transportation Future" (PDF). Natural Resources Defense Council. Retrieved on 2008-04-19.
  70. ^ Bartis, Jim, RAND Corporation (2006-10-26). "Unconventional Liquid Fuels Overview. 2006 Boston World Oil Conference" (PDF). Association for the Study of Peak Oil & Gas - USA. Retrieved on 2007-06-28.
  71. ^ a b Draft Oil Shale and Tar Sands Resource Management Plan Amendments to Address Land Use Allocations in Colorado, Utah, and Wyoming and Programmatic Environmental Impact Statement. Volume 2 (PDF). Argonne National Laboratory (2007-12-07). Retrieved on 2008-03-31.
  72. ^ Luken, Larry (2005-07-09). Oil Shale Myths. Shale Oil Information Center. Retrieved on 2008-04-01.
  73. ^ Critics charge energy, water needs of oil shale could harm environment. U.S. Water News Online (July 2007). Retrieved on 2008-04-01.
  74. ^ Hopes for shale oil are revived. worldoil.com (August 2005). Retrieved on 2008-04-01.
  75. ^ Oil-shale 'rush' is sparking concern. Deseret Morning News (2008-03-22). Retrieved on 2008-