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Oil shale


Oil shale refers to solid hydrocarbon (kerogen) rock resulting from a decomposed organic matter still at solid state, in a sedimentary rock unit.

The oil shale may also be called black shale.

Oil shale and shale oil must not be confused as they do not mean the same thing since shale oil designates tight oil or tight shale oil.


Oil shale and shale oil are different as oil shale is a rock as a variety of the shale rocks while shale oil is a light crude trapped in shale, limestone and sandstone formations characterized by very low porosity and permeability.

That is the reason why shale oil is better named tight oil or light tight oil (LTO) or tight shale oil.

The shale oil is normally found in the sedimentary formations as oil shale but at the state of light crude oil captured between the rock layers.

Instead, oil shale is a rock which contains hydrocarbon, oil in this case, and belongs to the large shale rock family.

Shale is a sedimentary rock which can be found in all sedimentary basins on earth.

As made of thin aggregated mineral particles, shale is classified as a mudstone.

Depending on the sedimentary basin where they lie, the shale may have different colors, red, brown, green and black.

The black shale contains hydrocarbons, that is why oil shale may also be called black shale.

Since this sedimentary rocks were produced by the addition and compression of sediments deposits laying on each other over millions years, the shale got a laminated and fissile structure.

The lamination represents the million of thin layers of sediments deposits.

Fissile indicates that these laminations are not linked between each other by other mean than the pressure under which they were maintained for million years.

Therefore these laminations may be separated easily under any mechanical action or in releasing the natural pressure which maintains them together.

This laminated and fissile structure of the shale guided researchers to develop the fracturing process in creating over pressure to separate the shale laminations.

Black shale or oil shale may contain up to 30% of solidi hydrocarbons or kerogen.

To extract the oil from the pores of the shale the laminations must be separated, for example by fractionation or hydraulic fracturing.

Then heating and the introduction of solvents improve the quantity of oil released by the shale and facilitates its collection back to the surface.

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