Shale oil

Oil shale was one of the first sources of mineral oil used by humans. In the 10th century, the Arabic physician Masawaih al-Mardini (Mesue the Younger) first described a method of extracting oil from "some kind of bituminous shale". It was also reported to have been used in Switzerland and Austria in the early 14th century. In 1596, the personal physician of Frederick I, Duke of Württemberg wrote of its healing properties. The British Crown granted a patent in 1694 to three persons who had "found a way to extract and make great quantities of pitch, tarr and oyle out of a sort of stone." Later sold as Betton's British Oil, the distilled product was said to have been "tried by diverse persons in Aches and Pains with much benefit." Modern shale oil extraction industries were established in France during the 1830s and in Scotland during the 1840s. The oil was used as fuel, as a lubricant and lamp oil; the Industrial Revolution had created additional demand for lighting. It served as a substitute for the increasingly scarce and expensive whale oil. During the late 19th century, shale-oil extraction plants were built in Australia, Brazil and the United States. China, Estonia, New Zealand, South Africa, Spain, Sweden and Switzerland produced shale oil in the early 20th century. The discovery of crude oil in the Middle East during mid-century brought most of these industries to a halt, although Estonia and Northeast China maintained their extraction industries into the early 21st century. ==Extraction process==

Shale oil is extracted by pyrolysis, hydrogenation, or thermal dissolution of oil shale. The pyrolysis of the rock is performed in a retort, situated either above ground or within the rock formation itself. As of 2008, most oil shale industries perform the shale oil extraction process after the rock is mined, crushed and transported to a retorting facility, although several experimental technologies perform the process in place. The temperature at which the kerogen decomposes into usable hydrocarbons varies with the time-scale of the process; in the above-ground retorting process decomposition begins at , but proceeds more rapidly and completely at higher temperatures. Decomposition takes place most quickly at a temperature between . Hydrogenation and thermal dissolution (reactive fluid processes) extract the oil using hydrogen donors, solvents, or a combination of these. Thermal dissolution involves the application of solvents at elevated temperatures and pressures, increasing oil output by cracking the dissolved organic matter. Different methods produce shale oil with different properties. A critical measure of the viability of extraction of shale oil lies in the ratio of the energy produced by the oil shale to the energy used in its mining and processing, a ratio known as "Energy Returned on Energy Invested" (EROEI). An EROEI of 2 (or 2:1 ratio) would mean that to produce 2 barrels of actual oil the equivalent in energy of 1 barrel of oil has to be burnt/consumed. A 1984 study estimated the EROEI of the various known oil-shale deposits as varying between 0.7 and 13.3. More recent studies estimates the EROEI of oil shales to be 1–2:1 or 2–16:1 – depending on whether self-energy is counted as a cost or internal energy is excluded and only purchased energy is counted as input. Royal Dutch Shell reported an EROEI of three to four in 2006 on its in situ development in the "Mahogany Research Project." The amount of oil that can be recovered during retorting varies with the oil shale and the technology used. The major global shale oil producers have published their yields for their commercial operations. Fushun Mining Group reports producing 300,000 tons per year of shale oil from 6.6 million tons of shale, a yield of 4.5% by weight. VKG Oil claims to produce 250,000 tons of oil per year from 2 million tons of shale, a yield of 13%. Petrobras produces in their Petrosix plant 550 tons of oil per day from 6,200 tons of shale, a yield of 9%. ==Properties==

The properties of raw shale oil vary depending on the composition of the parent oil shale and the extraction technology used. Like conventional oil, shale oil is a complex mixture of hydrocarbons, and is characterized according to the bulk properties of the oil. It usually contains large quantities of olefinic and aromatic hydrocarbons. It can also contain significant quantities of heteroatoms. A typical shale oil composition includes 0.5–1% of oxygen, 1.5–2% of nitrogen and 0.15–1% of sulfur; some deposits contain more heteroatoms than others. Mineral particles and metals are often present as well. Generally, the oil is less fluid than crude oil, becoming pourable at temperatures between , while conventional crude oil is pourable at temperatures between ; this property affects shale oil's ability to be transported in existing oil pipelines. Shale oil contains polycyclic aromatic hydrocarbons, which are carcinogenic. The US EPA has concluded that raw shale oil has a mild carcinogenic potential, comparable to some intermediate petroleum refinery products, while upgraded shale oil has lower carcinogenic potential, as most of the polycyclic aromatics are believed to have been broken down by hydrogenation. The World Health Organization classifies shale oil as a Group 1 carcinogen to humans. ==Upgrading==

Although raw shale oil can be immediately burnt as a fuel oil, many of its applications require that it be upgraded. The differing properties of the raw oils call for correspondingly various pre-treatments before it can be sent to a conventional oil refinery. Particulates in the raw oil clog downstream processes; sulfur and nitrogen create air pollution. Sulfur and nitrogen, along with the arsenic and iron that may be present, also destroy the catalysts used in refining. Olefins form insoluble sediments and cause instability. The oxygen within the oil, present at higher levels than in crude oil, lends itself to the formation of destructive free radicals. Phenols can be first removed by water extraction. Upgrading shale oil into transport fuels requires adjusting hydrogen–carbon ratios by adding hydrogen (hydrocracking) or removing carbon (coking). Shale oil produced by some technologies, such as the Kiviter process, can be used without further upgrading as an oil constituent and as a source of phenolic compounds. Distillate oils from the Kiviter process can also be used as diluents for petroleum-originated heavy oils and as an adhesive-enhancing additive in bituminous materials such as asphalt. ==Uses==

Before World War II, most shale oil was upgraded for use as transport fuels. Afterwards, it was used as a raw material for chemical intermediates, pure chemicals and industrial resins, and as a railroad wood preservative. As of 2008, it is primarily used as a heating oil and marine fuel, and to a lesser extent in the production of various chemicals. Additional cracking can create the lighter hydrocarbons used in gasoline. ==Reserves and production==

Global technically recoverable oil shale reserves have recently been estimated at of shale oil, with the largest reserves in the United States, which is thought to have . Worldwide production of shale oil was estimated at in 2008. The leading producers were China (), Estonia (), and Brazil (). In March 2011, the United States Bureau of Land Management called into question proposals for commercial operations in Colorado, Utah and Wyoming, stating that "(t)here are no economically viable ways yet known to extract and process oil shale for commercial purposes". The US Energy Information Administration sometimes uses the phrase "shale (tight) oil" to refer to tight oil, "crude oil ... produced directly from tight oil resources". In 2021, the US produced 7.23 million barrels of such tight oil each day, equal to about 64% of total U.S. crude oil production. The IEA also occasionally calls tight oil "shale oil", but classifies any products from oil shale with solid fuels. ==See also==