Claridge, Elmond L. Formerly, Chemical Engineering Department, University of Houston, Houston, Texas.
Okandan, Ender Department of Petroleum and Natural Gas Engineering, Middle East Technical University, Ankara, Turkey.
- Composition changes in refining
- Nature of oil reservoirs
- Heavy oil
- Links to Primary Literature
- Additional Readings
Unrefined, or crude, oil is found underground and under the seafloor, in the interstices between grains of sandstone and limestone or dolomite (not in caves). Petroleum is a mixture of liquids varying in color from nearly colorless to jet black, in viscosity from thinner than water to thicker than molasses, and in density from light gases to asphalts heavier than water. It can be separated by distillation into fractions that range from light color, low density, and low viscosity to the opposite extreme. In places where it has oozed from the ground, its volatile fractions have vaporized, leaving the dense, black parts of the oil as a pool of tar or asphalt (such as the Brea Tar Pits in California). Egyptians used such tar for embalming the dead, and Mesopotamians used it for adhering bricks together. Much of the world's crude oil is today produced from drilled wells. See also: Petroleum engineering
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