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Most of us know that gasoline has something to do with oil, yet we have no idea how it is “created.” Many of us also believe that oil (aka petroleum) is only for the use of automobiles or large machines. Nothing could be further from the truth!
Petroleum is a naturally occurring earth material that is a mixture of hydrocarbon compounds. Of organic origin, it is found in some porous sedimentary rocks and in many parts of the world. Petroleum is refined to give such a variety of products as gasoline, kerosene, fuel oil, lubricating oils, greases, waxes, and many industrial chemicals.
Most geologists think that petroleum, and the natural gas found with it, developed from the remains of minute animals and plants that were buried in silt, clay, or lime deposits in shallow seas and on the ocean bottoms near continents. Later deposits covered the matieral containing the plant-and-animal remains. Over great lengths of time the pressure of overlying sediments, the action of bacteria, and increased temperature helped to change the plant-and-animal remains to petroleum and natural gas. Changes in the earth's crust have caused the rocks in which petroleum formed to be tilted, folded, broken, and buried beneath other rocks.
Petroleum and natural gas commonly migrate upward through rocks until they come to some barrier they can neither penetrate nor avoid. Petroleum and gas accumulate beneath such barriers, and the places of accumulation are called oil traps. The impermeable rock over such an accumulation of oil is called a cap rock.
A reservoir rock commonly contains water, natural gas, and petroleum. In an oil trap the petroleum floats above water, and the natural gas occupies available space above the petroleum. The water is salt water (from the ancient sea).
The first step in finding oil is to study the geology of a region. If the geologic conditions are favorable for the formation and accumulation of oil, detailed exploration to find local oil traps is begun.
The most widely used method of exploration is the reflection technique of the seismic method. Small charges of dynamite are exploded in shallow holes to create small artificual earthquakes. The times taken by the shock waves to travel to a particular rock layer and back again are recorded by small seismographs. The depth of the rock layer can be determined from the travel time.
Two methods of oil drilling are employed: standard, or cable tool, drilling and rotary drilling. Rotary drilling is the common method. Cable tool drilling is used for drilling shallow wells and for corrective work on wells drilled with rotary equipment. For deep wells rotary drilling is much faster and more economical. The deepest oil wells are as much as 25,000 feet deep. The average depth of oil wells in the United States is about 4,000 feet.
A cable tool rig drills by the chipping action of a solid steel cylindrical bit raised and lowered by a cable to strike the bottom of the well hole. The chips of rock broken off mix with water or mud placed in the well hole and are removed at regular intervals by a bailer.
To drill an oil well with rotary equipment a derrick must be erected. A portable derrick, called a jack-knife derrick, may be used and removed when the well is drilled. THe derrick and related equipment are over a pit that contains blowout-prevention equipment. The power for drilling is transmitted from an engine to a rotary table. The rotary table, which is just above the floor of the derrick, is circular, with a square hole in its center.
Once a preliminary hole about a foot wide and a hundred feet deep has been drilled and lined with pipe set in cement, the main drilling operation begins. A bit is screwed onto a length of drill piope and is lowered into the hole. The drill pipe is attached to a square shaped hollow stem called a kelly. The kelly fits into the square hole in the rotary table and is attached to a swivel. The whole drill string is suspended from a hook attached to steel cables. The steel cables run over the top of the derrick and down to the draw works. When the rotary table turns, the kelly turns, and the drill pipe and bit down in the hole also turn. As the bit wears away rock in the well hole, the bit and drill string are lowered into the hole by the cable. Additional lengths of drill pipe are added to the drill string as needed.
During drilling a fluid, called drilling mud, is pumped into the swivel and through the hollow kelly and drill pipe to the bit. The mud is forced through jet holes in the bit and cuts soft rock and picks up drill cuttings. It also lubricates the bit and dissipates heat. It returns to the surface between the drill pipe and the well walls.
In a new well the expansion of gas mixed witht he petroleum or the pressure of water around the petroleum may force petroleum tot he surface. Such a well is called a flowing well. Most oil wells soon stop flowing unless this gas and water are reinjected (pressure maintenance). Otherwise the petroleum must be pumped out.
Petroleum is pumped from a well to temporary storage tanks at the well site. If the petroleum has a high gas content, it is passed through a separator tower, which separates the gas from the liquid. The gas may be sold, vented to the air and burned, or returned to the petroleum-producing formation.
Large quantities of crude petroleum are transported overland by pipelines. The pipelines run from major oilfields to large cities, to refineries, and to seaports.
Crude petroleum is a mixture of many hydrocarbon compounds. A hydrocarbon contains mostly hydrogen and carbon. Most petroleum comes from the ground as a black, greasy fluid, but some petroleums are green, brown, or light amber. A few crude petroleums are almost colorless. Besides simple hydrocarbons, crude petroleum may contain traces of nitrogen, sulfur, and oxygen.
Crude petrolem itself is not a useful substance, but the products into which it can be separated are extremely useful. The process of separating parts of crude petroleum from each other is called refining.
In all refineries the crude petroleum is first subjected to fractional distillation. The petroleum is heated in a pipe still to about 700 degrees F., and most of the petroleum becomes vapor. The vapor is discharged into a fractionating tower. The petroleum vapors discharged into the bottom of the fractionating tower rises through holes in trayes covered by bubble caps. The parts of the crude petroleum that have the highest boiling points condense in the bottom trays. Uncondensed vapors rise to higher trays. The petroleum fractions with lower boiling points condense in trays farther up the tower.
The fractions with the lowest boiling points, gasoline and other volatile portions of the petroleum, leave the top of the fractionating tower as vapors. They are converted to liquid in a separate condenser. The liquid that condenses in each tray is removed from the tower by a pipe. Some of the separated products obtained by fractional distillation are naphtha, gasoline, kerosene, fuel oil, and diesel fuel. A residue of crude petroleum is removed from the bottom of the tower.
The residual crude petroleum may be sent to a thermal cracking unit in the refinery. In a thermal cracking unit the petroleum is subjected to such intense heat and pressure over a long period of time that many molecules divide into smaller molecules. Some of the products of thermal cracking are gasoline, wet gas and unstable naphtha, and heavy fuel oils or coke. THe gas and naphtha may be sent to a polymerization unit.
If lubricating oils are to be manufactured from the residual crude petroleum, the crude is sent to a unit where it undergoes fractional distillation in vacuum.
Fuel oils, or gas oils, from the original fractional-distillation process may be sent to a catalytic cracking unit in a refinery. The fuel oil and a hot catalyst are mixed, and the fuel oil molecules break up into smaller molecules. SOme of the products of a catalytic cracking unit are gases (such as propane and butane), gasolines, light fuel oil, and heavy fuel oil. High octane automobile gasoline and aviation gasoline are produced by this method.
Gasoline is the principal petroleum product. About 45 percent of the petroleum products of refineries in the United States is gasoline. Kerosene comprises about 5 percent of the products manufactured from crude petroleum. Before 1900 the only important product of petroleum was kerosene, which was used as lamp oil. About 37 percent of the crude petroleum refined in the United States is converted to different weights of fuel oils. Fuel oils include heating oils for domestic furnaces, diesel fuels, heavy oils for oil burners in factories, and bunker fuel, used in the boiler firing of ships. Lubricants, oils, and greases make up about 4 percent of petroleum products.
Many other petroleum products are important. Naphtha and benzene are used as solvents. Petroleum jelly, a highly refined grease, is used in medical ointments and cosmetics. About 94 percent of the wax made in the United States is made from petroleum. Petroleum coke, a byproduct of refining, is made into carbon electrodes used in the electrolytic production of aluminum. Asphalt is the solid or semi-solid residue from vacuum or steam distillation of asphalt-base crude petroleum. It is used in road paving mixtures and in roofing materials. Road oils, used for road surfacing, are heavy distillate oils and crude petroleum. Liquified refinery gases are used as raw materials by chemical plants.
Sources:
en.wikipedia.org/wiki/Petroleum
science.howstuffworks.com/gasoline2.htm
www.factsonfuel.org/gasoline/index.html
www.earthguide.ucsd.edu/fuels/uses.html
Sergio King