Oil shale
Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen, a solid mixture of organic chemical compounds. This substance differs from bitumen-impregnated rocks and humic coals because its maturation does not exceed early mesocatagenetic stages. Geologists classify oil shales based on their composition as carbonate-rich shales, siliceous shales, or cannel shales. The mineral matter in these deposits includes various fine-grained silicates and carbonates like quartz, feldspar, clay, calcite, and dolomite. In commercial grades, the ratio of organic matter to mineral matter lies approximately between 0.75:5 and 1.5:5. Organic components derive from algae, spores, pollen, plant cuticles, and cellular debris from aquatic and land plants. Some deposits contain significant fossils, such as those found in Germany's Messel Pit, which holds UNESCO World Heritage Site status. A classification scheme developed by Adrian C. Hutton between 1987 and 1991 designates oil shales as terrestrial, lacustrine, or marine based on the environment of initial biomass deposit. Known oil shales are predominantly of aquatic origin, either marine or lake-bottom-deposited.
A 2016 estimate set total world resources of oil shale equivalent to yield of 4 trillion barrels of shale oil. The largest resource deposits occur in the United States within the Green River Formation, covering portions of Colorado, Utah, and Wyoming. About 70% of this U.S. resource lies on land owned or managed by the federal government. Deposits in the United States constitute more than 80% of world resources, with other significant holders being China, Russia, and Brazil. Only 33 countries possess known deposits of potential economic value. Well-explored deposits potentially classifiable as reserves include the Green River deposits, Tertiary deposits in Queensland Australia, and sites in Sweden, Estonia, Jordan, 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 using the Fischer Assay. Analysts distinguish between oil shale resources and oil shale reserves, where resources refer to all deposits while reserves represent those extractable economically using existing technology. Since extraction technologies develop continuously, planners can only estimate the amount of recoverable kerogen.
Humans have used oil shale as a fuel since prehistoric times because 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 polish them to create ornaments. 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. Modern industrial mining began in 1837 in Autun, France, followed by exploitation in Scotland, Germany, and several other countries. Scottish production peaked around 1913 operating 120 oil shale works and producing 3,332,000 tonnes of oil shale. This generated around 2% of global petroleum production at that time. Operations during the 19th century focused on kerosene, lamp oil, and paraffin to supply growing demand for lighting during the Industrial Revolution. On the 2nd of May 1982, known as Black Sunday, Exxon canceled its US$5 billion Colony Shale Oil Project near Parachute, Colorado. This cancellation laid off more than 2,000 workers and left a trail of home foreclosures and small business bankruptcies. Following the 1973 oil crisis, world production reached a peak of 46 million tonnes in 1980 before falling to about 16 million tonnes in 2000.
Most exploitation involves mining followed by shipping elsewhere after which the shale is burned directly or undergoes further processing. The most common methods involve open-pit mining and strip mining to expose deposits occurring near the surface. Underground mining employs the room-and-pillar method to remove less overlying material. Extraction usually takes place above ground through ex-situ processing, though newer technologies perform this underground via in-situ processing. Pyrolysis converts kerogen into shale oil and gas by heating shale in absence of oxygen between 250°C and 500°C. In-situ processing heats oil shale underground without removing it first. Such technologies can potentially extract more oil from a given area since they access material at greater depths than surface mines. Explosives rubblize the deposit for modified in-situ retorting to create permeability for gas flow. By 2006 only four technologies remained in commercial use: Kiviter, Galoter, Fushun, and Petrosix. Hundreds of patents exist for oil shale retorting but only a few dozen have undergone testing. Most conversion technologies involve heating shale to decompose kerogen into gas, condensable oil, and solid residue.
A 2005 survey conducted by the RAND Corporation estimated producing a barrel of oil at a surface retorting complex would range between US$70, 95 adjusted to 2005 values. This estimate considers varying levels of kerogen quality and extraction efficiency. To run a profitable operation, crude oil prices must remain above these levels. The International Energy Agency estimated investment and operating costs would be similar to Canadian oil sands, meaning economic viability requires prices above $60 per barrel. A critical measure of viability lies in energy return on investment ratios known as EROI. A 1984 study estimated EROI of various known deposits varied between 0.7, 13.3 while development projects assert an EROI between 3 and 10. World Energy Outlook 2010 stated ex-situ processing typically yields 4 to 5 while in-situ may be as low as 2. However most used energy can be provided by burning spent shale or oil-shale gas. In 2010 the IEA noted carbon pricing adds additional cost, with New Policies Scenario introducing $50 per tonne emission adding $7.50 cost per barrel.
Mining oil shale involves numerous environmental impacts more pronounced in surface mining than underground operations. These include acid drainage induced by sudden rapid exposure and subsequent oxidation of formerly buried materials. Introduction of metals including mercury into surface-water and groundwater occurs alongside increased erosion and sulfur-gas emissions. Atmospheric emissions from processing include carbon dioxide, a greenhouse gas that creates even more pollution than conventional fossil fuels. Water concerns are sensitive issues in arid regions like western U.S. and Israel's Negev Desert where plans exist to expand despite water shortages. Above-ground retorting uses between one and five barrels of water per barrel of produced shale-oil. A 2008 programmatic environmental impact statement issued by the U.S. Bureau of Land Management stated surface mining produces 3 cubic meters of waste water per tonne of processed oil shale. Environmental activists including members of Greenpeace have organized strong protests against the industry. One result was Queensland Energy Resources putting the proposed Stuart Oil Shale Project on hold in 2004. Commonly detected water contaminants include quinoline derivatives, pyridine, and various alkyl homologues of pyridine such as picoline and lutidine.
Common questions
What is oil shale and how does it differ from other rocks?
Oil shale is an organic-rich fine-grained sedimentary rock containing kerogen, a solid mixture of organic chemical compounds. This substance differs from bitumen-impregnated rocks and humic coals because its maturation does not exceed early mesocatagenetic stages.
Where are the largest oil shale resources located in the world?
The largest resource deposits occur in the United States within the Green River Formation, covering portions of Colorado, Utah, and Wyoming. Deposits in the United States constitute more than 80% of world resources, with other significant holders being China, Russia, and Brazil.
When did humans first start using oil shale as a fuel source?
Humans have used oil shale as a fuel since prehistoric times because it generally burns without any processing. Around 3000 BC, rock oil was used in Mesopotamia for road construction and making architectural adhesives.
How much oil can be extracted from one tonne of oil shale according to industry standards?
These deposits have given rise to expectations of yielding at least 40 liters of shale oil per tonne using the Fischer Assay. Analysts distinguish between oil shale resources and oil shale reserves, where resources refer to all deposits while reserves represent those extractable economically using existing technology.
What environmental impacts result from mining oil shale in arid regions?
Mining oil shale involves numerous environmental impacts more pronounced in surface mining than underground operations including acid drainage induced by sudden rapid exposure and subsequent oxidation of formerly buried materials. Above-ground retorting uses between one and five barrels of water per barrel of produced shale-oil.