Shale oil is an unconventional oil produced from oil shale rock fragments by pyrolysis, hydrogenation, or thermal dissolution. These processes convert the organic matter within the rock (kerogen) into synthetic oil and gas. The resulting oil can be used immediately as a fuel or upgraded to meet refinery feedstock specifications by adding hydrogen and removing impurities such as sulfur and nitrogen. The refined products can be used for the same purposes as those derived from crude oil. The term "shale oil" is also used for crude oil produced from shales of other unconventional, very low permeability formations. However, to reduce the risk of confusion of shale oil produced from oil shale with crude oil in oil-bearing shales, the term "tight oil" is preferred for the latter. The International Energy Agency recommends to use the term "light tight oil" and World Energy Resources 2013 report by the World Energy Council uses the term "tight oil" for crude oil in oil-bearing shales.
History
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. Shale oil was used to light the streets of Modena, Italy at the turn of the 18th century. 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. In response to rising petroleum prices at the turn of the 21st century, extraction operations have commenced, been explored, or been renewed in the United States, China, Australia and Jordan.
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 300 °C (570 °F), but proceeds more rapidly and completely at higher temperatures. Decomposition takes place most quickly at a temperature between 480 and 520 °C (900 and 970 °F). 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. About one sixth of the oil shales in the Green River Formation have a relatively high yield of 25 to 100 US gallons (95 to 379 L; 21 to 83 imp gal) of shale oil per ton of oil shale; about one third yield from 10 to 25 US gallons (38 to 95 L; 8.3 to 20.8 imp gal) per ton. (Ten US gal/ton is approximately 3.4 tons of oil per 100 tons of shale.) About half of the oil shales in the Green River Formation yield less than 10 US gal/ton. 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%.
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