petroleum
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petroleum,
oily, flammable liquid that occurs naturally in deposits, usually beneath the surface of the earth; it is also called crude oil. It consists principally of a mixture of hydrocarbonshydrocarbon, any organic compound composed solely of the elements hydrogen and carbon. The hydrocarbons differ both in the total number of carbon and hydrogen atoms in their molecules and in the proportion of hydrogen to carbon.
..... Click the link for more information. , with traces of various nitrogenous and sulfurous compounds.
Origin and Natural Occurrence
During the past 600 million years incompletely decayed plant and animal remains have become buried under thick layers of rock. It is believed that petroleum consists of the remains of these organisms but it is the small microscopic plankton organism remains that are largely responsible for the relatively high organic carbon content of fine-grained sediments like the Chattanooga shale which are the principle source rocks for petroleum. Among the leading producers of petroleum are Saudi Arabia, Russia, the United States (chiefly Texas, North Dakota, Alaska, and California), China, Iran, Canada, the United Arab Emirates, Mexico, Brazil, Kuwait, Iraq, Nigeria, Venezuela, and Norway. The largest proven reserves are in the Middle East, but the United States and Russia also have large reserves.
Exploration and Drilling of Wells
Because of the subterranean origin of petroleum it must be extracted by means of wellswell,
aperture in the earth's surface through which substances in a natural underground reservoir, such as water, gas, oil, salt, and sulfur, can flow or be pumped to the surface. In the United States, until some years after the Civil War, the majority of wells were "open," i.e.
..... Click the link for more information. . Until an exploratory well, or wildcat, has been dug, there is no sure way of knowing whether or not petroleum lies under a particular site. In order to reduce the number of exploratory wells drilled, scientific methods are used to pick the most promising sites. Sensitive instruments, such as the gravimeter, the magnetometer, and the seismograph, may be used to find subsurface rock formations that can hold crude oil. Drilling is a fairly complex and often risky process. Some wells must be dug several miles deep before petroleum deposits are reached. Many are now drilled offshore from platforms standing in the ocean bed. Usually the petroleum from a new well will come to the surface under its own pressure. Later the crude oil must be pumped out or forced to the surface by injecting water, air, natural gas, steam, carbon dioxide, or another substance into the deposits. Enhanced recovery techniques have increased the percentage of oil that can be extracted from a field.
Composition and Refining of Petroleum
The physical properties and exact chemical composition of crude oil varies from one locality to another. The different hydrocarbon components of petroleum are dissolved natural gasnatural gas,
natural mixture of gaseous hydrocarbons found issuing from the ground or obtained from specially driven wells. The composition of natural gas varies in different localities.
..... Click the link for more information. , gasoline, benzinebenzine
, colorless, highly flammable liquid. It is used as a cleaning agent because it is a solvent for organic substances such as fats, oils, and resins and is also used in the preparation of certain dyes and paints.
..... Click the link for more information. , naphthanaphtha
, term usually restricted to a class of colorless, volatile, flammable liquid hydrocarbon mixtures. Obtained as one of the more volatile fractions in the fractional distillation of petroleum (when it is known as petroleum naphtha), in the fractional distillation of coal
..... Click the link for more information. , kerosenekerosene
or kerosine,
colorless, thin mineral oil whose density is between 0.75 and 0.85 grams per cubic centimeter. A mixture of hydrocarbons, it is commonly obtained in the fractional distillation of petroleum as the portion boiling off between 150°C; and
..... Click the link for more information. , diesel fuel and light heating oils, heavy heating oils, and finally tars of various weights (see tar and pitchtar and pitch,
viscous, dark-brown to black substances obtained by the destructive distillation of coal, wood, petroleum, peat, and certain other organic materials. The heating or partial burning of wood to make charcoal yields tar as a byproduct and is an ancient method for the
..... Click the link for more information. ). The crude oil is usually sent from a well to a refinery in pipelines (see under pipepipe,
hollow structure, usually cylindrical, for conducting materials. It is used primarily to convey liquids, gases, or solids suspended in a liquid, e.g., a slurry. It is also used as a conduit for electric wires.
..... Click the link for more information. ) or tanker ships.
The hydrocarbon components are separated from each other by various refining processes. In a process called fractional distillationdistillation,
process used to separate the substances composing a mixture. It involves a change of state, as of liquid to gas, and subsequent condensation. The process was probably first used in the production of intoxicating beverages.
..... Click the link for more information. petroleum is heated and sent into a tower. The vapors of the different components condense on collectors at different heights in the tower. The separated fractions are then drawn from the collectors and further processed into various petroleum products. One of the many products of crude oil is a light substance with little color that is rich in gasolinegasoline
or petrol,
light, volatile mixture of hydrocarbons for use in the internal-combustion engine and as an organic solvent, obtained primarily by fractional distillation and "cracking" of petroleum, but also obtained from natural gas, by destructive distillation
..... Click the link for more information. . Another is a black tarry substance that is rich in asphaltasphalt
, brownish-black substance used commonly in road making, roofing, and waterproofing. Chemically, it is a natural mixture of hydrocarbons. It varies in consistency from a solid to a semisolid, has great tenacity, melts when heated, and when ignited will burn with a smoky
..... Click the link for more information. .
As the lighter fractions, especially gasoline, are in the greatest demand, so-called cracking processes have been developed in which heat, pressure, and certain catalysts are used to break up the large molecules of heavy hydrocarbons into small molecules of light hydrocarbons. Some of the heavier fractions find eventual use as lubricating oils, paraffinsparaffin,
white, more-or-less translucent, odorless, tasteless, waxy solid. It melts between 47°C; and 65°C; and is insoluble in water but soluble in ether, benzene, and certain esters. Paraffin is unaffected by most common chemical reagents but burns readily in air.
..... Click the link for more information. , and highly refined medicinal substances such as petrolatumpetrolatum
, colorless to yellowish-white hydrocarbon mixture obtained by fractional distillation of petroleum. In its jellylike semisolid form (known as petroleum jelly and also by several trade names) it is used in preparing medicinal ointments and for lubrication.
..... Click the link for more information. .
See also petrochemicalspetrochemical,
any one of a large group of chemicals derived from a component of petroleum or natural gas. The cracking processes for manufacturing gasoline produce vast quantities of gaseous hydrocarbons.
..... Click the link for more information. .
History and Development of Petroleum
Petroleum has been known throughout historical time. It was used in mortar, for coating walls and boat hulls, and as a fire weapon in defensive warfare. Native Americans used it in magic and medicine and in making paints. Pioneers bought it from the Native Americans for medicinal use and called it Seneca oil and Genesee oil. In Europe it was scooped from streams or holes in the ground, and in the early 19th cent. small quantities were made from shale. In 1815 several streets in Prague were lighted with petroleum lamps.
The modern petroleum industry began in 1859, when the American oil pioneer E. L. DrakeDrake, Edwin Laurentine,
1819–80, American oil well driller, b. Greene co., N.Y. In 1858 he was employed to conduct drilling operations and on Aug. 27, 1859, he struck oil near Titusville, Pa., at a depth of 69.5 ft (21.2 m).
..... Click the link for more information. drilled a producing well on Oil Creek in Pennsylvania at a place that later became Titusville. Many wells were drilled in the region. Kerosene was the chief finished product, and kerosene lamps soon replaced whale oil lamps and candles in general use. Little use other than as lamp fuel was made of petroleum until the development of the gasoline engine and its application to automobiles, trucks, tractors, and airplanes. Today the world is heavily dependent on petroleum for motive power, lubrication, fuel, dyes, drugs, and many synthetics. The widespread use of petroleum has created serious environmental problems. The great quantities that are burned as fuels generate most of the air pollutionpollution,
contamination of the environment as a result of human activities. The term pollution refers primarily to the fouling of air, water, and land by wastes (see air pollution; water pollution; solid waste).
..... Click the link for more information. in industrialized countries, and oil spilled from tankers and offshore wells has polluted oceans and coastlines.
See also energy, sources ofenergy, sources of,
origins of the power used for transportation, for heat and light in dwelling and working areas, and for the manufacture of goods of all kinds, among other applications.
..... Click the link for more information. ; oil industryoil industry,
the business of discovering oil (petroleum), extracting it from the ground, refining it into a variety of products, and distributing it to the public. The development of the oil industry in the 19th and 20th cent.
..... Click the link for more information. .
Bibliography
See K. K. Landes, Petroleum Geology of the United States (1970); S. Schackne and N. D. Drake, Oil for the World (2d ed. 1960); L. Mosley, Power Play: Oil in the Middle East (1973).