Oil shale Totally Explained

Oil shale is a fine-grained sedimentary rock, containing significant amounts of kerogen (a solid mixture of organic chemical compounds), from which liquid hydrocarbons can be manufactured. The name oil shale is something of a misnomer as the rock isn't necessarily a shale and the hydrocarbon in it isn't truly oil. Deposits of oil shale are located around the world, including major deposits in the United States. Global deposits are estimated as equivalent to 2.9–3.3 trillion (2.9–3.3 x 10¹²) barrels of recoverable oil.
The kerogen in oil shale can be converted to synthetic crude oil through the chemical process of pyrolysis. When heated to a sufficiently high temperature a vapor is driven off which can be distilled (retorted) to yield a petroleum-like shale oil—a form of non-conventional oil—and combustible shale gas (shale gas can also refer to gas occurring naturally in shales). Oil shale can also be burnt directly as a low-grade fuel for power generation and heating purposes, and be used as a raw material in the chemical and construction materials industries.

Geology

Oil shale is an organic-rich sedimentary rock, differentiated from bitumen-impregnated rocks (tar sands and petroleum reservoir rocks), humic coals and carbonaceous shale. Depending on their composition, oil shales are classified into three categories, namely carbonate-rich shale, siliceous shale and cannel shale. Oil shales are also classified according to their kerogen type, which is a function of the hydrogen, carbon and oxygen content of the organic matter.

Reserves

Although oil shale resources occur in many countries, only 33 countries possess deposits of possible economic value. The largest deposits in the world are found in the United States in the Green River basin, which covers portions of Colorado, Utah, and Wyoming; about 70 % of this resource is located on federally-owned or managed land. Total world resources of oil shale are estimated at 411 gigatons (411 x 10⁹ tonnes), which is enough to yield 2.9 to 3.3 trillion (2.9 to 3.3 x 10¹²) U.S. barrels.

History

The various attempts to develop the world's oil shale deposits, over a period of over 150 years, have experienced successes when the cost of shale oil production in a given region was less than the price of crude oil or its other substitutes. According to a survey conducted by the RAND Corporation, a surface retorting complex (comprising a mine, retorting plant, upgrading plant, supporting utilities, and spent shale reclamation) is unlikely to be profitable in the United States until crude oil prices range between US$70 to US$95 per barrel (in 2005 dollars). Royal Dutch Shell has announced that its in-situ extraction technology in Colorado could be competitive at prices over US$30 per barrel, while other technologies at full-scale production assert profitability at oil prices even lower than US$20 per barrel. To increase the efficiency of oil shale retorting, several co-pyrolysis processes have been proposed and tested.
A critical measure of the viability of oil shale as an energy source is the ratio of the energy produced by the shale to the energy used in its mining and processing, a ratio known as "Energy Returned on Energy Invested" (EROEI). A 1984 study estimated the EROEI of the various known oil shale deposits as varying between 0.7-13.3. Royal Dutch Shell has reported an EROEI of three to four on its in-situ development, Mahogany Research Project. An additional economic consideration is the water needed in the oil shale retorting process, which may pose a problem in areas with water scarcity.

Environmental considerations

The oil shale industry can have a negative impact on the surrounding environments, if the risks associated with it are not managed correctly. Environmental concerns raised over the extraction of shale oil have caused the oil shale industry in some countries to come to a halt. Opposition to the proposed Stuart Oil Shale Project in Australia resulted in its being put on hold in 2004.
Surface-mining of oil shale deposits has the same environmental impacts as those of open-pit mining. In addition, combustion and thermal processing generate waste material, and the atmospheric emissions include carbon dioxide, a major greenhouse gas. Experimental in-situ conversion processes and carbon capture and storage technologies may reduce some of these concerns in the future, but they may at the same time may cause other problems, including groundwater pollution.

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