Gas & Oil

Petroleum (from Greek petra – rock and elaion – oil or Latin oleum – oil ), crude oil, sometimes colloquially called black gold or "Texas Tea", is a thick, dark brown or greenish liquid. more...

Petroleum exists in the upper strata of some areas of the Earth's crust. It consists of a complex mixture of various hydrocarbons, largely of the alkane series, but may vary much in appearance, composition, and purity. Petroleum is used mostly, by volume, for producing fuel oil, which is an important "primary energy" source (IEA Key World Energy Statistics). Petroleum is also the raw material for many chemical products, including solvents, fertilizers, pesticides, and plastics.

Formation

Biogenic theory

Most geologists view crude oil, like coal and natural gas, as the product of compression and heating of ancient vegetation over geological time scales. According to this theory, it is formed from the decayed remains of prehistoric marine animals and terrestrial plants. Over many centuries this organic matter, mixed with mud, is buried under thick sedimentary layers of material. The resulting high levels of heat and pressure cause the remains to metamorphose, first into a waxy material known as kerogen, and then into liquid and gaseous hydrocarbons in a process known as catagenesis. These then migrate through adjacent rock layers until they become trapped underground in porous rocks called reservoirs, forming an oil field, from which the liquid can be extracted by drilling and pumping. 150m is generally considered the "oil window". Though this corresponds to different depths for different locations around the world, a 'typical' depth for an oil window might be 4 - 5 km. Three conditions must be present for oil reservoirs to form: a rich source rock, a migration conduit, and a trap (seal) that forms the reservoir.

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