Petroleum geochemistry
Petroleum geochemistry is a branch of geochemistry which deals specifically with petroleum and its origin, generation, and accumulation, as well as its extraction, refinement, and use. Petroleum, also known as crude oil, is a solid, liquid, and/or gaesous mix of hydrocarbons. These hydrocarbons are from the burial and metamorphosis of organic matter from millions of years ago; the organic matter is from marine animals, plants, and algae. Petroleum is extracted from the Earth, refined, and used as an energy source.
Crude oil is most commonly organised into four types - light, heavy, sweet, and sour. Petroleum is a non-renewable energy source, 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.
Types of Petroleum
Petroleum is differentiated into types based on its American Petroleum Institute gravity and by how much sulphur it contains.API Gravity
The API gravity of a crude oil is a measurement of purity - i.e., amount of impurities, such as sulphur, nitrogen, or oxygen. Impurities increase the density of the crude.Light Crude Oil
Light crude oils have higher API gravity figures, due to having fewer impurities. It is more commonly used to produce diesel and gasoline than heavier oils are. Due to its lower viscosity, it is easier to extract and to transport.Heavy Crude Oil
Heavy crude oils have lower API gravity figures, and a larger percentage of impurities. It is used in the making of heavier outputs - e.g., asphalt - and has a higher viscosity, making it more difficult to transport and extract.Sulphur Content
How 'sweet' or 'sour' a crude oil is is based on the amount of sulphur it contains.Sweet Crude Oil
'Sweet' crude oil has lower sulphur content - lower than 0.5%. It can be refined into kerosene, high-quality diesel, and gasoline.Sour Crude Oil
'Sour' crude oil has high natural sulphur content. Extra treatment is required in the refining process; impurities are removed to refine the crude into gasoline. Due to the greater cost associated, it is more commonly refined into fuel oil and diesel - less valuable outputs than products of sweet crude oil.Hydrocarbon Compounds
The three main hydrocarbon compounds in petroleum are paraffins, naphthenes, and aromatics.Paraffins
Paraffinic hydrocarbons are part of the alkane series, and are the most common hydrocarbon found in crude oil. Paraffins are often a part of gasoline, making them comparatively more valuable.Paraffinic hydrocarbons are also known as alkanes, and are represented by the formula CnH2n+2, where n is a positive integer.
Naphthenes
Naphthenic hydrocarbons are saturated cyclic hydrocarbons, and are very important in the refining of liquid crude oil.Also known as cyclic alkanes, they are represented by the formula CnH2n, where n is a positive integer.
Aromatics
Aromatic hydrocarbons are cyclic, and are much less abundant than the other two main hydrocarbon compounds. They are represented by the formula CnHn, where n is a positive integer.Petroleum Geochemical Techniques
Techniques are used for finding the source rock, as well as the type and amount of the petroleum within. They are also used to note migration timing and pathways, which are then used to predict when and where petroleum can be found; petroleum sources can be predicted if material associated with source rock is found.Surface Prospecting
Petroleum, or evidence of its immediate occurrence, can be found on the surface of the Earth. Oil seeps can be found near a fault zone, where the movement of Earth's crust can expose petroleum source rock, and thus the crude oil itself. They can also be found on the ocean floor, and can be found using satellite imaging.[Distillation]
While not used as commonly as other techniques today, distillation is used in the process of refining petroleum. It involves the dividation of the crude oil into hydrocarbon categories, and products are recovered from the heated material. A distillation tower is used in separation of the oil, with anywhere between 2 and 300 theoretical plates.Gas Chromatography">Gas chromatography">Gas Chromatography
Similar to the process of distillation, gas-liquid chromatography utilises a distillation tower to separate the petroleum. However, compared to distillation's 2 to 300 theoretical plates, gas chromatography includes more than 25,000. This provides a greater degree of separation.In order to achieve more complete analyses, gas chromatography is used along with mass spectrometry, with infrared spectrometry, and with isotope ratio mass spectrometry.