Oil and natural gas drilling and wells
Background (Encyclopedia of Global Resources)
Oil and natural gas are recovered through drilled wells that are designed and constructed to ensure many years of service. These wells may vary from a few hundred meters to more than 6,000 meters in depth. They must recover oil and gas from their reservoirs in the subsurface. The location of the well is determined by an exploration team, which produces maps of the subsurface showing possible accumulation of oil and gas. A team of land agents investigates the ownership of the drill location and provides information so that the right to produce the oil and gas can be secured from the landowner—be it an individual, a state, the federal government, or a foreign nation. After the right to drill is secured, the drilling plan is converted into action.
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Drilling Procedures (Encyclopedia of Global Resources)
A suitable drilling rig is selected through the solicitation of information from drilling companies. After selection and transportation to the drilling site, the rig is positioned over the marked location, which has been accurately determined by surveying instruments. A drill bit is connected to drill pipe and drill collars. Drill collars are thick-walled cylinders about 9 meters in length used immediately above the drill bit to prevent the bit from wandering as it cuts through rock formations of varying strength and inclination. The drill pipe and collars are rotated by a rotary table at the surface, causing the drill bit to rotate. The weight of the drill string, as the downhole assembly is called, along with its rotation, causes the rock underneath the bit to be crushed. This crushed rock is circulated to the surface by drilling fluid. This fluid, called “mud,” is a mix of chemicals suited to the downhole environment. It is pumped down the well through the drill string, through the bit nozzles, and then back up to the surface in the annular space between the drill string and the wall of the drilled hole.
The drill bit eventually becomes dull and must be replaced. When this happens, the drill string must be unscrewed so that the bit can be brought to the surface. This process is called “tripping the bit.” The drilled hole must be lined with steel casing to prevent slumping of the borehole wall and unwanted...
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Hazards (Encyclopedia of Global Resources)
During the drilling of a well, potential hazards must be recognized by the drilling personnel. These include blowouts and lost circulation. A blowout is the uncontrolled escape of subsurface fluids to the surface. These spectacular events have been identified with the oil and gas industry since its beginnings, and they remain as one of its most newsworthy subjects. A properly drilled well should not encounter a blowout if adequate diagnosis and detection are made. The weight of the drilling fluid may be increased to control abnormal pressures in the subsurface. Blowout preventers, a type of valving used with the drilling rig, are designed to protect against blowouts until the well can be controlled and drilling resumed without spoiling the surface area adjacent to the well.
Lost circulation involves drilling fluid that is lost because it seeps into the pore space or fractures in the subsurface rock formations. If enough drilling fluid escapes downhole, well control can be lost and a blowout can occur. Lost circulation is controlled by decreasing the weight of the drilling fluid or using plugging agents circulated into the subsurface leak zones.
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Oil and Gas Pumping and Production (Encyclopedia of Global Resources)
When the well has been completed and production is assured, a wellhead is installed to replace the blowout preventers. The wellhead, nicknamed the “Christmas tree,” is a series of valves designed to seal the casing, its annular space, and the tubing to prevent leaks.
Crude oil is processed at the site only to remove unwanted foreign matter. Surface equipment used to process oil and gas includes dehydrators to remove water and water vapor, and separators to remove foreign matter, including rock particles, paraffin, and other debris prohibited by the buyer of the oil and gas. Large tanks are used to store oil prior to delivery.
Oil is transported by pipeline, truck, and train to the refinery for further breakdown into gasolines, motor oils, and other products and chemicals. Natural gas is odorized by placing a distinctive odorant in it, and its pressure is elevated by compression for delivery to the customer through a series of pipelines.
An ideal oil and gas well will flow to the surface using its internal energy. Oil wells eventually reach the point where their flowing energy is depleted and they must be pumped in order to continue producing. A variety of pumps have been used in the oil and gas industry; among them is the familiar beam pump, sometimes called a “horse’s head” or “nodding donkey,” that is seen in oil-producing areas around the world.
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Depletion and Economic Limit (Encyclopedia of Global Resources)
When a well’s energy is depleted, an enhanced oil recovery (EOR) project may be started. EOR techniques are used to produce additional oil from an oil and gas formation that has depleted its primary energy source. Various fluids ranging from fresh water to exotic liquids, gases, and even steam are injected into oil-producing rocks to force more oil from them. Often EOR projects can produce an amount of oil equivalent to that recovered during the well’s primary operating life.
All oil and gas wells eventually reach their “economic limit,” at which point economic production ceases. The economic limit is an arbitrary production rate that depends on the expenses associated with producing the well, the percentage of ownership of the well’s operator, and the price of the oil and gas. This limit may be reached in a short period after production begins for poorly performing wells, or it may exceed fifty years. Once the production rate falls below the economic limit, the well is either plugged and abandoned (cement plugs are used to seal the wellbore) or converted into a liquid disposal or EOR injection well. After the well’s operators have plugged the wellbore to the satisfaction of regulatory authorities, the surface location in the vicinity of the well is restored in an environmentally acceptable manner. Little or no trace of the well itself should be left.
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Further Reading (Encyclopedia of Global Resources)
Beggs, H. Dale. Gas Production Operations. Tulsa, Okla.: OGCI, 1984.
Boomer, Paul M. A Primer of Oilwell Drilling. 7th ed. Austin, Tex.: Petroleum Extension Service, University of Texas, 2008.
Devereux, Steve. Drilling Technology in Nontechnical Language. Tulsa, Okla.: PennWell, 1999.
Economides, Michael J., A. Daniel Hill, and Christine Ehlig-Economides. Petroleum Production Systems. Englewood Cliffs, N.J.: PTR Prentice Hall, 1994.
Hyne, Norman J. Nontechnical Guide to Petroleum Geology, Exploration, Drilling, and Production. 2d ed. Tulsa, Okla.: PennWell, 2001.
Miesner, Thomas O., and William L. Leffler. Oil and Gas Pipelines in Nontechnical Language. Tulsa, Okla.: PennWell, 2006.
Moore, Preston L. Drilling Practices Manual. 2d ed. Tulsa, Okla.: PennWell, 1986.
Nind, T. E. W. Principles of Oil Well Production. 2d ed. New York: McGraw-Hill, 1981.
How Stuff Works. How Oil Drilling Works. http://science.howstuffworks.com/oil-drilling5.htm
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