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Oil shale formation takes place in a number of depositional settings and has considerable compositional variation. Oil shales can be classified by their composition (carbonate minerals such as calcite or detrital minerals such as quartz and clays) or by their depositional environment (large lakes, shallow marine, and lagoon/small lake settings).
Approximately 30% of the world's oil is found in these shale deposits. Although the origin of these deposits is still under study, it has been established that the shale routinely overlies glacial and glacio-marine sediment deposited ~445 million years before the present by the Hirnantian glaciation. The shale has been linked to glacial ...
The largest deposits are found in the remains of large lakes such as the deposits of the Green River Formation of Wyoming and Utah, USA. Large lake oil shale basins are typically found in areas of block faulting or crustal warping due to mountain building. Deposits such as the Green River may be as much as 2,000 feet (610 m) and yield up to 40 ...
The current surface of the Messel pit is roughly 60 m (200 ft) below the local land and is about 0.7 km 2 (0.27 sq mi) in area. The oil-shale bed originally extended to a depth of 190 m (620 ft). [5] 47 million years ago in the Eocene when the Messel deposits formed, the area was 10° further south than it is now.
The fine particles that compose shale can remain suspended in water long after the larger particles of sand have been deposited. As a result, shales are typically deposited in very slow moving water and are often found in lakes and lagoonal deposits, in river deltas, on floodplains and offshore below the wave base. [13]
A 1984 study estimated the EROI of the various known oil-shale deposits as varying between 0.7–13.3, [75] although known oil-shale extraction development projects assert an EROI between 3 and 10. According to the World Energy Outlook 2010, the EROI of ex-situ processing is typically 4 to 5 while of in-situ processing it may be even as low as 2.
Fossils (various bryozoans) in Ordovician period kukersite oil shale, northern Estonia. Estonian kukersite deposits are one of the world's highest-grade deposits with organic content varying from 15% to 55% with average more than 40%, and it has 65–67% conversion ratio into shale oil and oil shale gas. [1] [11] Fischer Assay oil yield is 30 ...
Oil exudes from joint cracks in the petroliferous shale forming the floor of mine. 1906 photo, U.S. Geological Survey Bulletin 321 Tar bubble at La Brea Tar Pits, California A petroleum seep is a place where natural liquid or gaseous hydrocarbons escape to the Earth's atmosphere and surface, normally under low pressure or flow.