Oil Shale

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.