About Oil Shale
Oil shale is a naturally occurring rock characterized by a high organic content. Because of the high organic matter within the rock it is also called a bituminous rock. Although called oil shale it is not always a shale but sometimes it is a high organic content limestone, chalk or other type of rock so a bituminous shale or bituminous limestone etc. are also prevalent names.
The origin of the organic matter within the rock is from the time of its deposit. During the time of deposition an organically enriched environment prevailed usually in marine or limnic conditions that contained various life forms (both from animal or plant origin). Another important feature of these rocks is that they are thermally immature, that is that they have not been buried under high temperatures and pressures for a very long time and therefore yield oil only by heating thus differentiating them from tight oil reservoirs which require fracking for oil production (well known as shale oil in the USA).
Oil shale extraction technologies and methods
The value of Oil Shale is in its ability to provide energy from its organic content. Currently there are 3 main modes in which Oil Shale is utilized:
Direct Combustion – In this mode Oil Shale is used by direct combustion in a similar mode as Coal to produce electricity in power stations. This method is practiced today in several countries like Estonia, China, Germany and Israel.
Ex-situ extraction of shale oil relates to above ground retorting of oil shale by pyrolysis hydrogenation or thermal dissolution. In this method the oil shale is mined, crushed, heated up and processed in closed systems. The oil produced is similar to crude oil. Today this method is practiced in few countries (Estonia, China, Brazil) commercially in modest capacities.
In most places direct combustion to generate electricity and shale oil extraction are done simultaneously which proved also to be energetically most efficient and economic.
In-situ shale oil extraction relates to underground retorting of oil shale by heating up deep oil shale layers. The shale oil is recovered through vertical wells drilled into the formation.
This method addresses mainly the exploitation of deep oil shale layers. No commercial experience has been reported yet.