Petroleum (L. petroleum, from Greek πετρέλαιον, lit. "rock oil") or crude oil is a naturally occurring, flammable liquid found in rock formations in the Earth consisting of a complex mixture of hydrocarbons of various molecular weights, plus other organic compounds.
Origin
Geologists view crude oil and natural gas as the product of compression and heating of ancient organic materials (i.e. kerogen) over geological time. Formation of petroleum occurs from hydrocarbon pyrolysis, in a variety of mostly endothermic reactions at high temperature and/or pressure. Today's oil formed from the preserved remains of prehistoric zooplankton and algae, which had settled to a sea or lake bottom in large quantities under anoxic conditions (the remains of prehistoric terrestrial plants, on the other hand, tended to form coal). Over geological time the organic matter mixed with mud, and was buried under heavy layers of sediment resulting in high levels of heat and pressure (known as diagenesis). This caused the organic matter to chemically change, first into a waxy material known as kerogen which is found in various oil shales around the world, and then with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis.
Composition
The proportion of hydrocarbons in the mixture is highly variable and ranges from as much as 97% by weight in the lighter oils to as little as 50% in the heavier oils and bitumens.
The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic hydrocarbons while the other organic compounds contain nitrogen, oxygen and sulfur, and trace amounts of metals such as iron, nickel, copper and vanadium. The exact molecular composition varies widely from formation to formation but the proportion of chemical elements vary over fairly narrow limits as follows (Element's Percent range):
- Carbon: 83 to 87%
- Hydrogen: 10 to 14%
- Nitrogen: 0.1 to 2%
- Oxygen: 0.1 to 1.5%
- Sulfur: 0.5 to 6%
- Metals: less than 1000 ppm
| Hydrocarbons | Range | ||||||
| Paraffins | 15 to 60% | ||||||
| Naphthenes | 30 to 60% | ||||||
| Aromatics | 3 to 30% | ||||||
| Asphaltics | remainder |
Application
Due to its high energy density, easy transportability and relative abundance, oil has become the world's most important source of energy since the mid-1950s. Petroleum is also the raw material for many chemical products, including pharmaceuticals, solvents, fertilizers, pesticides, and plastics; the 16% not used for energy production is converted into these other materials.
References:
- Gasoline FAQ. FAQ.org. Retreived on 1 June 2009 from http://www.faqs.org/faqs/autos/gasoline-faq/part1/
- Petroleum. Wikipedia. Retreived on 1 June 2009 from http://en.wikipedia.org/wiki/Petroleum
- Petroleum. Britannica Encyclopedia. Retreived on 1 June 2009 from http://www.britannica.com/EBchecked/topic/454269/petroleum/50706/Origin-of-crude-oil
Book Recommendation:
Standard Handbook of Petroleum and Natural Gas Engineering, Second Edition (Complementary Science)
By William C. Lyons PhD PE , Gary J Plisga BS
