Some oil seeps to the Earth's surface: this was used by the early Mesopotamian civilizations. But most petroleum is extracted via oil wells from reservoirs in the Earth's crust sealed by upfolds of impermeable rock or by salt domes which form traps. The first oil well was drilled in western Pennsylvania in 1859. The industry thus begun has grown so fast that it now supplies about half the world's energy, as well as the raw materials for petrochemicals.
Modern technology has made possible oil-well drilling to a depth of 5 km, and deep-sea wells in 150 m of water. Rotary drilling is used, with pressurized mud to carry the rock to the surface and to prevent escape of oil. When the well is completed, the oil rises to the surface, usually under its own pressure, though pumping may be required. After removing salt and water, the petroleum is refined by fractional distillation, producing the fractions gasoline, kerosene, diesel oil, fuel oil, lubricating oil, and asphalt (see fractionation). Undesirable compounds may be removed by solvent extraction, treatment with sulfuric acid, etc., and less valuable components converted into more valuable ones by cracking, reforming, alkylation, and polymerization. The chemical composition of crude petroleum is chiefly alkane's, saturated alicyclic compounds, and aromatic compounds, with some sulfur compounds, oxygen compounds (carboxylic acids and phenols), nitrogen, and salt.
Related categories INDUSTRIAL CHEMISTRY
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