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what is it? Sometimes known as “the rock that burns”, oil shale is sedimentary rock that is rich in kerogen, a solid tar-like material, which becomes a liquid when heated. It can be burned in its rocky form straight from the ground, or oil and gas can be extracted using a process called ‘retorting’. This is done either after the oil shale has been mined, where it is crushed up and refined, or ‘in-situ’ (in place) underground by directly heating the deposit and extracting the resulting liquid, which then requires further processing. The ‘oil’ produced from oil shale, sometimes referred to as synthetic crude, synfuel or shale oil (see below) is of lower quality and contains less energy than conventional crude oil. Global resources are estimated at 4.8 trillion barrels.1
Oilshale OILY ROCK THAT CAN BE BURNED, OR PROCESSED TO PRODUCE A LIQUID FUEL. EXTREMELY INEFFICIENT AS A FUEL, RESULTS IN VERY HIGH GREENHOUSE GAS EMISSIONS AND SERIOUS WATER POLLUTION.
Oil shale or shale oil?
Oil shale has been used as a fuel for thousands of years, initially burned directly as a source of heat and later to produce steam and electricity. It was not until the mid 19th century in France and Scotland that it was used to produce oil on an industrial scale. As crude oil extraction increased after the Second World War, oil shale became less attractive as a fuel source. Production of synthetic crude from oil shale peaked following the 1973 oil crisis and then fell sharply. It is only recently, with high oil prices, increasing scarcity of conventional crude, and countries’ increasing concern over energy security, that there has been a resurgence in interest in oil shale. Oil shales vary significantly in terms of the quantity of kerogen and the other substances they contain, some of which can be commercially extracted along with the oil shale. Uranium, vanadium, zinc, alumina, phosphate, sodium carbonate minerals, ammonium sulphate, and sulphur are all sometimes found in oil shales.2
Confusingly, ‘shale oil’ can refer to the liquid fuel extracted from ‘oil shale’ by heating it (this was always the traditional meaning of the term), or to oil extracted from shale rock using techniques such as fracking. The second definition began being used when the US boom in shale gas resulted in shale formations also being exploited for oil (see separate ‘Shale Oil’ factsheet for more information). A great deal of confusion and disagreement persists, but many have started to use the term ‘tight oil’ to refer to oil extracted from shale formations using horizontal drilling and fracking. Even more confusingly, the term ‘oil shale’, which usually means the oily rock rich in kerogen being discussed in this factsheet, is also sometimes used to refer to shale formations which contain oil. Baffled? Well, you’re not alone!