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A blowout is the uncontrolled release of crude oil and/or natural gas from an oil well or gas well after pressure control systems have failed.〔'All About Blowout', R. Westergaard, Norwegian Oil Review, 1987 ISBN 82-991533-0-1〕 Modern wells have special blowout preventers to prevent such an occurrence. Prior to the advent of pressure control equipment in the 1920s, the uncontrolled release of oil and gas from a well while drilling was common and was known as an oil gusher, gusher or wild well. An accidental spark during a blowout can lead to a catastrophic oil or gas fire. == History == Gushers were an icon of oil exploration during the late 19th and early 20th centuries. During that era, the simple drilling techniques such as cable-tool drilling and the lack of blowout preventers meant that drillers could not control high-pressure reservoirs. When these high pressure zones were breached, the oil or natural gas would travel up the well at a high rate, forcing out the drill string and creating a gusher. A well which began as a gusher was said to have "blown in": for instance, the Lakeview Gusher ''blew in'' in 1910. These uncapped wells could produce large amounts of oil, often shooting 200 feet (60 m) or higher into the air.〔http://www.sjgs.com/lakeview.html〕 A blowout primarily composed of natural gas was known as a ''gas gusher''. Despite being symbols of new-found wealth, gushers were dangerous and wasteful. They killed workmen involved in drilling, destroyed equipment, and coated the landscape with thousands of barrels of oil; additionally, the explosive concussion released by the well when it pierces an oil/gas reservoir has been responsible for a number of oilmen losing their hearing entirely; standing too near to the drilling rig at the moment it drills into the oil reservoir is extremely hazardous. The impact on wildlife is very hard to quantify, but can only be estimated to be mild in the most optimistic models—realistically, the ecological impact is estimated by scientists across the ideological spectrum to be severe, profound, and lasting. To complicate matters further, the free flowing oil was—and is—in danger of igniting.〔http://www.rootsweb.com/~txnavarr/business/oil_industry/hughes_and_mckie_oil_well_fire/index.htm〕 One dramatic account of a blowout and fire reads, With a roar like a hundred express trains racing across the countryside, the well blew out, spewing oil in all directions. The derrick simply evaporated. Casings wilted like lettuce out of water, as heavy machinery writhed and twisted into grotesque shapes in the blazing inferno.〔http://aoghs.org/technology/end-of-gushers/〕 The development of rotary drilling techniques where the density of the drilling fluid is sufficient to overcome the downhole pressure of a newly penetrated zone meant that gushers became avoidable. If however the fluid density was not adequate or fluids were lost to the formation, then there was still a significant risk of a well blowout. In 1924 the first successful blowout preventer was brought to market.〔http://www.asme.org/Communities/History/Landmarks/First_RamType_Blowout.cfm〕 The BOP valve affixed to the wellhead could be closed in the event of drilling into a high pressure zone, and the well fluids contained. Well control techniques could be used to regain control of the well. As the technology developed, blowout preventers became standard equipment, and gushers became a thing of the past. In the modern petroleum industry, uncontrollable wells became known as blowouts and are comparatively rare. There has been significant improvement in technology, well control techniques, and personnel training which has helped to prevent their occurring.〔 From 1976 to 1981, 21 blowout reports are available.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Blowout (well drilling)」の詳細全文を読む スポンサード リンク
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