Oil shale
Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen from which liquid hydrocarbons can be produced. In addition to kerogen, general composition of oil shales constitutes inorganic substance and bitumens. Based on their deposition environment, oil shales are classified as marine, lacustrine and terrestrial oil shales. Oil shales differ from oil-bearing shales, shale deposits that contain petroleum that is sometimes produced from drilled wells. Examples of oil-bearing shales are the Bakken Formation, Pierre Shale, Niobrara Formation, and Eagle Ford Formation. Accordingly, shale oil produced from oil shale should not be confused with tight oil, which is also frequently called shale oil.
A 2016 estimate of global deposits set the total world resources of oil shale equivalent of of oil in place. Oil shale has gained attention as a potential abundant source of oil. 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.
Oil shale can be burned directly in furnaces as a low-grade fuel for power generation and district heating or used as a raw material in chemical and construction-materials processing. Heating oil shale to a sufficiently high temperature causes the chemical process of pyrolysis to yield a vapor. Upon cooling the vapor, the liquid unconventional oil, called shale oil, is separated from combustible 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. Oil-shale mining and processing raise a number of environmental concerns, such as land use, waste disposal, water use, waste-water management, greenhouse-gas emissions and air pollution.
Geology
Oil shale, an organic-rich sedimentary rock, belongs to the group of sapropel fuels. 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 shales in the strict sense. 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". Their common defining feature is low solubility in low-boiling organic solvents and generation of liquid organic products on thermal decomposition. Geologists can classify oil shales on the basis of their composition as carbonate-rich shales, siliceous shales, or cannel shales.Oil shale differs from bitumen-impregnated rocks, humic coals and carbonaceous shale. While oil sands do originate from the biodegradation of oil, heat and pressure have not transformed the kerogen in oil shale into petroleum, which means its maturation does not exceed early mesocatagenetic. 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 Formation. Accordingly, shale oil produced from oil shale should not be confused with tight oil, which is called also frequently shale oil.
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. 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 approximately 1.2 to 1.8 times lower than for crude oil and about 1.5 to 3 times higher than for coals. The organic components of oil shale derive 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. Some deposits contain significant fossils; Germany's Messel Pit has the status of a UNESCO World Heritage Site. The mineral matter in oil shale includes various fine-grained silicates and carbonates. Inorganic matrix can contain quartz, feldspar, clay, carbonate, pyrite and some other minerals.
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. The most commonly used classification of oil shales, developed between 1987 and 1991 by Adrian C. Hutton, adapts petrographic terms from coal terminology. This classification designates oil shales as terrestrial, lacustrine, or marine, based on the environment of the initial biomass deposit. Known oil shales are predominantly of aquatic origin. Hutton's classification scheme has proven useful in estimating the yield and composition of the extracted oil.
Resource
As source rocks for most conventional oil reservoirs, oil shale deposits are found in all world oil provinces, although most of them are too deep to be exploited economically. 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. Although resources of oil shale occur in many countries, only 33 countries possess known deposits of potential economic value. Well-explored deposits, potentially classifiable 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, southern Mongolia and Russia. These deposits have given rise to expectations of yielding at least 40 liters of shale oil per tonne of oil shale, using the Fischer Assay.A 2016 estimate set the total world resources of oil shale equivalent to yield of of shale oil, with the largest resource deposits in the United States accounting more than 80% of the world total resource. For comparison, at the same time the world's proven oil reserves are estimated to be. 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. Deposits in the United States constitute more than 80% of world resources; other significant resource holders being China, Russia, and Brazil. The amount of economically recoverable oil shale is unknown.
History
Humans have used oil shale as a fuel since prehistoric times, since it generally burns without any processing. Around 3000 BC, "rock oil" was used in Mesopotamia for road construction and making architectural adhesives. Britons of the Iron Age used tractable oil shales to fashion cists for burial, or just polish it to create ornaments.In the 10th century, the Arab physician Masawaih al-Mardini described a method of extraction of oil from "some kind of bituminous shale". 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".
Modern industrial mining of oil shale began in 1837 in Autun, France, followed by exploitation in Scotland, Germany, and several other countries. 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, supplied from Scottish oil shales. Fuel oil, lubricating oil and grease, and ammonium sulfate were also produced. Scottish production peaked in around 1913, operating 120 oil shale works, producing 3,332,000 tonnes of oil shale, generating around 2% of the global production of petroleum. 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.
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. 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, because of competition from cheap conventional petroleum in the 1980s.
On 2 May 1982, known in some circles as "Black Sunday", Exxon canceled its US$5 billion Colony Shale Oil Project near Parachute, Colorado, because of low oil prices and increased expenses, laying off more than 2,000 workers and leaving a trail of home foreclosures and small business bankruptcies. 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.
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.