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 Modern wells have blowout preventers intended to prevent such an occurrence. An accidental spark during a blowout can lead to a catastrophic oil or gas fire.
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.
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 or higher into the air. 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. 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.
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. However, if 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. 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, only 21 blowouts occurred.
Notable gushers A blowout in 1815 resulted from an attempt to drill for salt rather than for oil. Joseph Eichar and his team were digging west of the town of Wooster, Ohio, US along Killbuck Creek, when they struck oil. In a written retelling by Eichar's daughter, Eleanor, the strike produced "a spontaneous outburst, which shot up high as the tops of the highest trees!" Oil drillers struck a number of gushers near Oil City, Pennsylvania, US in 1861. The most famous was the Little & Merrick well, in Rouseville, which began gushing oil on 17 April 1861. The spectacle of the fountain of oil flowing out at about 3,000 barrels (480 m3) per day had drawn a significant crowd, some of whom stood in the raining oil. That same evening, the rig caught fire, killing between 15 and 19 people, and injuring at least 13 more. Other early gushers in northwest Pennsylvania were the Phillips #2 (4,000 barrels (640 m3) per day) in September 1861, and the Woodford well (3,000 barrels (480 m3) per day) in December 1861. The Shaw Gusher in Oil Springs, Ontario, was Canada's first oil gusher. On January 16, 1862, it shot oil from over below ground to above the treetops at a rate of per day, triggering the oil boom in Lambton County. Lucas Gusher at Spindletop in Beaumont, Texas, US in 1901 flowed at per day at its peak, but soon slowed and was capped within nine days. The well tripled U.S. oil production overnight and marked the start of the Texas oil industry., Texas State Historical Association Masjed Soleiman, Iran, in 1908 marked the first major oil strike recorded in the Middle East. Dos Bocas in the State of Veracruz, Mexico, was a famous 1908 Mexican blowout that formed a large crater. It leaked oil from the main reservoir for many years, continuing even after 1938 (when Pemex nationalized the Mexican oil industry). Lakeview Gusher on the Midway-Sunset Oil Field in Kern County, California, US of 1910 is believed to be the largest-ever U.S. gusher. At its peak, more than of oil per day flowed out, reaching as high as in the air. It remained uncapped for 18 months, spilling over of oil, less than half of which was recovered. A short-lived gusher at Alamitos #1 in Signal Hill, California, US in 1921 marked the discovery of the Long Beach Oil Field, one of the most productive oil fields in the world. The Barroso 2 well in Cabimas, Venezuela, in December 1922 flowed at around per day for nine days, plus a large amount of natural gas.http://www.propuestas.reacciun.ve/Servidor_Tematico_Petroleo/documentos_articulos6.html#petroleo7 Baba Gurgur near Kirkuk, Iraq, an oilfield known since antiquity, erupted at a rate of a day in 1927. The Yates #30-A in Pecos County, Texas, US gushing 80 feet through the fifteen-inch casing, produced a world record 204,682 barrels of oil a day from a depth of 1,070 feet on 23 September 1929. The Wild Mary Sudik gusher in Oklahoma City, Oklahoma, US in 1930 flowed at a rate of per day. The Daisy Bradford gusher in 1930 marked the discovery of the East Texas Oil Field, the largest oilfield in the contiguous United States. The largest known 'wildcat' oil gusher blew near Qom, Iran, on 26 August 1956. The uncontrolled oil gushed to a height of , at a rate of per day. The gusher was closed after 90 days' work by Bagher Mostofi and Myron Kinley (USA). On October 17, 1982, a sour gas well Amoco Dome Brazeau River, 13-12-48-12, being drilled 20 km west of Lodgepole, Alberta blew out. The burning well was finally capped 67 days later by the Texas well-control company Boots & Coots. One of the most troublesome gushers happened on 23 June 1985, at well #37 at the Tengiz field in Atyrau, Kazakh SSR, Soviet Union, where the 4,209-metre deep well blew out and the 200-metre high gusher self-ignited two days later. Oil pressure up to 800 atm and high hydrogen sulfide content had led to the gusher being capped only on 27 July 1986. The total volume of erupted material measured at 4.3 million metric tons of oil and 1.7 billion m³ of natural gas, and the burning gusher resulted in 890 tons of various mercaptans and more than 900,000 tons of soot released into the atmosphere. Deepwater Horizon explosion: The largest underwater blowout in U.S. history occurred on 20 April 2010, in the Gulf of Mexico at the Macondo Prospect oil field. The blowout caused the explosion of the Deepwater Horizon, a mobile offshore drilling platform owned by Transocean and under lease to BP at the time of the blowout. While the exact volume of oil spilled is unknown, , the United States Geological Survey Flow Rate Technical Group has placed the estimate at between of crude oil per day.
Causes
Reservoir pressure
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights, and other organic compounds, found in geologic formations beneath the Earth's surface. Because most hydrocarbons are lighter than rock or water, they often migrate upward and occasionally laterally through adjacent rock layers until either reaching the surface or becoming trapped within porous rocks (known as reservoirs) by impermeable rocks above. When hydrocarbons are concentrated in a trap, an oil field forms, from which the liquid can be extracted by drilling and pumping. The downhole pressure in the rock structures changes depending upon the depth and the characteristics of the source rock. Natural gas (mostly methane) may be present also, usually above the oil within the reservoir, but sometimes dissolved in the oil at reservoir pressure and temperature. Dissolved gas typically comes out of solution as free gas as the pressure is reduced either under controlled production operations or in a kick, or in an uncontrolled blowout. The hydrocarbon in some reservoirs may be essentially all natural gas.
Formation kick The downhole fluid pressures are controlled in modern wells through the balancing of the hydrostatic pressure provided by the mud column. Should the balance of the drilling mud pressure be incorrect (i.e., the mud pressure gradient is less than the formation pore pressure gradient), then formation fluids (oil, natural gas, and/or water) can begin to flow into the wellbore and up the annulus (the space between the outside of the drill string and the wall of the open hole or the inside of the casing), and/or inside the drill pipe. This is commonly called a kick. Ideally, mechanical barriers such as blowout preventers (BOPs) can be closed to isolate the well while the hydrostatic balance is regained through circulation of fluids in the well. But if the well is not shut in (common term for the closing of the blow-out preventer), a kick can quickly escalate into a blowout when the formation fluids reach the surface, especially when the influx contains gas that expands rapidly with the reduced pressure as it flows up the wellbore, further decreasing the effective weight of the fluid.
Early warning signs of an impending well kick while drilling are: Sudden change in drilling rate; Reduction in drillpipe weight; Change in pump pressure; Change in drilling fluid return rate.
Other warning signs during the drilling operation are: Returning mud "cut" by (i.e., contaminated by) gas, oil or water; Connection gases, high background gas units, and high bottoms-up gas units detected in the mudlogging unit.Grace, R: Blowout and Well Control Handbook, p. 42. Gulf Professional Publishing, 2003
The primary means of detecting a kick while drilling is a relative change in the circulation rate back up to the surface into the mud pits. The drilling crew or mud engineer keeps track of the level in the mud pits and closely monitors the rate of mud returns versus the rate that is being pumped down the drill pipe. Upon encountering a zone of higher pressure than is being exerted by the hydrostatic head of the drilling mud (including the small additional frictional head while circulating) at the bit, an increase in mud return rate would be noticed as the formation fluid influx blends in with the circulating drilling mud. Conversely, if the rate of returns is slower than expected, it means that a certain amount of the mud is being lost to a thief zone somewhere below the last casing shoe. This does not necessarily result in a kick (and may never become one); however, a drop in the mud level might allow influx of formation fluids from other zones if the hydrostatic head is reduced to less than that of a full column of mud.
Well control