- Related Topics:
- shale oil
- kerogen
- pyrobitumen
- Pumpherston process
- tasmanite
-
What is oil shale?
Oil shale is a sedimentary rock containing solid organic material that yields petroleum products and by-products when heated to around 300 °C without oxygen, a process called pyrolysis. The resulting liquid can be refined into fuels like diesel and gasoline, while solids can yield sulfur, alumina, and soda ash.
Oil shale forms from sediments in ancient lakes, seas, and bogs, resulting in deposits of varying thickness and mineral composition, including marlstone and mudstone. Major deposits are found worldwide, with significant resources in the United States, China, and Estonia. However, extracting oil from shale poses environmental challenges, including greenhouse gas emissions, water consumption, and land disturbance.
1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How is oil shale different from regular crude oil?
Oil shale and crude oil differ in their formation and extraction. Oil shale is a sedimentary rock containing solid organic matter that, when heated, yields petroleum products, whereas crude oil is liquid petroleum found in porous rock formations.
To extract shale oil, oil shale is heated to release liquid and gaseous hydrocarbons, a process called pyrolysis. In contrast, crude oil is extracted from the earth directly from rock formations. The kerogen found in oil shale is not distinct from the kerogen of petroleum source rocks.
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
Where is oil shale usually found in the world?
Oil shale deposits are found in over 30 countries worldwide. However, its economic development has been attractive only for brief periods since the early 20th century.
Developed oil shale formations include the kukersite deposits of northern Estonia, extending into northwest Russia, the Fushun deposits of northeast China, and the Irati Formation of southern Brazil. The large and rich Green River Formation (GRF) in the western United States has also attracted commercial interest periodically, depending on the price of conventional crude oil.
Oil shale was formed from sediments laid down in ancient lakes, seas, and small terrestrial water bodies such as bogs and lagoons.
1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How does oil form inside oil shale rocks?
Oil shale forms from sediments deposited in ancient bodies of water like lakes, seas, bogs, and lagoons. The organic matter in oil shale is mainly kerogen, a waxy mixture of hydrocarbon compounds that is the primary organic component of oil shale.
Kerogen originates from compacted organic material such as algae and plant life that accumulated at the bottom of ancient lakes and seas and was buried at great depths over long periods. Over time, pressure and heat transform this organic matter into kerogen, a solid material trapped within the rock.
The richest oil shale ranges from brown to black in color, has low density, is flammable, and is quite resistant to the oxidizing effects of air.
5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What methods are used to extract oil from oil shale?
Oil extraction from oil shale involves heating the rock to liberate hydrocarbons through a process called pyrolysis. This can be done aboveground (ex situ) in retorts or by heating the rock underground (in situ).
Aboveground methods involve mining and crushing the oil shale, then heating it in retorts at temperatures between 480–550 °C (900–1,020 °F) in an oxygen-free environment. In situ processing heats the rock underground, maximizing production, a slow process that can take months or years. The pyrolysis reactions occur at lower temperatures, roughly 325–400 °C (620–750 °F), producing a lighter oil and a higher gas-to-oil ratio.
Specific methods vary by heating approach, including internal combustion, hot-recycled-solids, conduction through a wall, externally generated hot gas, reactive fluids, and volumetric heating.
2 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are the environmental impacts of mining and using oil shale?
The environmental impacts of mining and using oil shale include greenhouse gas emissions, water consumption and pollution, surface disturbance, and socioeconomic effects.
Oil shale processing emits carbon dioxide, a greenhouse gas, through heating methods that involve hydrocarbon combustion. In situ processes emit at least 10 to 20 percent more CO2 than conventional petroleum production, while some aboveground processes may produce 50 percent more CO2.
Full-scale oil shale processing requires 0.7 to 1.2 liters of water for every liter of oil produced, primarily for site remediation, drilling or mining, and upgrading of the synthetic crude. Mining and retorting operations can contaminate surface water or groundwater, and in situ retorting may leave behind organic compounds that could contaminate groundwater reservoirs.
Large amounts of rock material have to be moved in open-pit or underground operations, which can adversely affect the integrity of the land, grazing and agricultural activities, and local fauna and flora. The development of oil shale on an industrial scale would affect the rural regions where the resources occur. Local governments might experience difficulty in meeting the demand for increased services and infrastructure before royalty revenues arrive from the new development.
1 Britannica SourceCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
oil shale, any sedimentary rock containing various amounts of solid organic material that yields petroleum products, along with a variety of solid by-products, when subjected to pyrolysis—a treatment that consists of heating the rock to above 300 °C (about 575 °F) in the absence of oxygen. The liquid oil extracted from oil shale, once it is upgraded, creates a type of synthetic crude oil that is commonly referred to as shale oil. Oil produced from oil shales has potential commercial value in some of the same markets served by conventional crude oil, as it can be refined into products ranging from diesel fuel to gasoline (petrol) to liquefied petroleum gas (LPG). Some of the solid by-products of oil shale processing are unusable wastes, but others have commercial value. These include sulfur, ammonia, alumina, soda ash, and nahcolite (a mineral form of sodium bicarbonate). In addition, spent shale has been used in the production of cement, where the carbon-rich material can enhance the energy balance of the mixture. At the same time, oil shale production has a potentially significant impact on the natural environment, including carbon emission, water consumption, groundwater contamination, and disturbance of land surfaces.
Some confusion has arisen over the terms oil shale and shale oil. Until the early 21st century, those terms respectively referred solely to the organic-rich petroleum source rock described in this article and to the liquid product obtained from this rock through pyrolysis. In the early 2000s, however, the same terms were applied also to fine-grained impermeable rocks that contain crude oil and to the oil produced from those rocks through hydraulic fracturing.
Formation and composition of oil shales
Geologic origins
Oil shale was formed from sediments laid down in ancient lakes, seas, and small terrestrial water bodies such as bogs and lagoons. Oil shales deposited in large lake basins, particularly those of tectonic origin, are commonly of considerable thickness in parts. Mineralogically, the deposits are composed of marlstone or argillaceous mudstone, possibly associated with volcanic tuff and evaporite mineral deposits. Major oil shale deposits of this type are the huge Green River Formation (GRF) in the western United States, dating from the Eocene Epoch; oil shales found in the Democratic Republic of the Congo that were laid down in the Triassic Period; and the Albert shale in New Brunswick, Canada, of Mississippian origin.
" height="20" alt="HEW Logo">
Oil shale deposited in shallow marine environments is thinner than shale of lacustrine origin but of greater areal extent. The mineral fraction is mostly clay and silica, though carbonates also occur. Extensive deposits of black shales of this variety were formed during the Cambrian Period in northern Europe and Siberia; the Silurian Period in North America; the Permian Period in southern Brazil, Uruguay, and Argentina; the Jurassic Period in western Europe; and the Miocene Epoch of the Neogene Period in Italy, Sicily, and California.
Oil shale deposited in small lakes, bogs, and lagoons is found associated with coal seams. Deposits of this type occur in a sequence found in western Europe dating from the Permian Period and in deposits of northeastern China laid down in the early Cenozoic Era.
Chemical composition
Oil shales consist of solid organic matter entrained in an inorganic mineral matrix. Chemically, the mineral content consists primarily of silicon, calcium, aluminum, magnesium, iron, sodium, and potassium found in silicate, carbonate, oxide, and sulfide minerals.
The chemical composition of the organic matter is variable. It consists mainly of complex organic molecules containing hydrogen and carbon as well as certain amounts of the heteroatomic elements oxygen, nitrogen, and sulfur. The heteroatomic elements have important effects on the properties of the oil extracted from shales, frequently influencing the choice of upgrading and refining processes, and shales from different regions and different geologic origins are sometimes known for the content of those crucial elements. For instance, the kukersite oil shale of Estonia is noted for being oxygen-rich. Oil shale that originated in saline lake environments, such as the GRF shales of the western United States, tends to be nitrogen-rich, whereas marine oil shales such as those found in Morocco, Egypt, Israel, and Jordan are sulfur-rich.
The trusted destination for professionals, college students, and lifelong learners.
SUBSCRIBE
Mineral content
The mineral constituents of oil shale vary according to sediment type. Some are true shale in which clay minerals are predominant, such as the Garden Gulch Member of the GRF in Utah. Others, such as the Parachute Creek Member of the GRF in Colorado, are marlstones, containing dolomite or calcite as well as silicate minerals such as clay, quartz, and feldspar.
The various oil shale deposits that have been mined around the world since the early 20th century have ranged from shale to marlstone to carbonate mudstone. All are relatively fine-grained sedimentary rocks, as deposits of coarse sediment such as sand are not compatible with the preservation of organic material. Sandstone found in the Wyoming part of the GRF, for instance, significantly reduces the organic richness of the oil shale.
In the GRF, saline minerals such as nahcolite, trona, and dawsonite, along with a host of other unusual minerals, were most likely formed under extremely saline and stratified conditions in the water of an Eocene lake. The chemical stratification would have created an oxygen-depleted, carbon dioxide-rich environment in the salty bottom layers of the lake, which would have helped to preserve the organic matter, deposit the inorganic minerals, and break down much of the clay carried in as sediment.