Petroleum geochemistry

[5] Petroleum is extracted from the Earth (above or below its surface, depending on the geology of the formation), refined, and used as an energy source.

[6] Petroleum is a non-renewable energy source (also known as a "fossil fuel"), so the efficacy of extraction and refining is important for its continued use; multiple techniques are used to detect and to extract crude oil, based on the source rock it is found in and the type of oil itself.

[7] The API gravity of a crude oil is a measurement of purity - i.e., amount of impurities, such as sulphur, nitrogen, or oxygen.

[9][6] Light crude oils have higher API gravity figures, due to having fewer impurities.

[9] Heavy crude oils have lower API gravity figures, and a larger percentage of impurities.

It involves the dividation of the crude oil into hydrocarbon categories, and products are recovered from the heated material.

Pyrolysis is used to characterise kerogens (insoluble hydrocarbons)[18] and asphaltenes (limited solubility in common solvents).

[20] Hydrous pyrolysis is performed within water and in high pressures; this method can simulate different depths of burial, demonstrating the possibilities of the fate of the source rock and the associated patroleum.

[16][21] With credit to the previously listed techniques, biomarkers were found in petroleum and source rock extract.

[16] Before the use of gas chromatography-mass spectrometry and biomarkers, correlation of locations' geology was used to find how different formations relate to each other and to their environment.