A top kill is a procedure used to regain control of an oil well that is experiencing a blowout in which crude oil or natural gas is unexpectedly erupting from the well. To stop the flow of uncontrolled gas and oil, heavyweight drilling mud is pumped into the well, creating a temporary sealing of the well.[1]
The method has been used with varying levels of success, most notably during the Deepwater Horizon oil spill of 2010 in which it failed to successfully contain the oil leaking into the Gulf of Mexico.[1]
Typical usage and procedure
editThe top kill method involves pumping liquid drilling fluid into the blowout preventer and main shaft of a well. As the density of the drilling fluid is greater than the oil or gas escaping from the well, the hydrostatic pressure of the drilling fluid exerts a force on the escaping oil mixture. When this force exceeds that of the escaping oil, the well is effectively plugged.[2]
After being plugged with drilling fluid, the well is permanently capped with cement. This ensures a long-term seal that is not dependent on the pressure of the well or drilling fluid.
The top kill method is typically used to stop leaking oil and gas wells that are either on the surface or at minimal depths underwater. This limitation is created primarily by the need to access the blowout preventer and well shaft, which becomes difficult as water depth increases. Divers, which would typically inspect the blowout preventer and attach necessary pipes, have to be replaced by remotely operated vehicles (ROVs).[1]
Usage in Iraq and Kuwait
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At the close of the Gulf War, retreating Iraqi military forces set fire to over 700 oil wells in Kuwait as part of a scorched earth policy.[3] The Kuwaiti government eventually contracted private organizations to extinguish these fires and cap the wells.[4]
In many cases, after extinguishing the flames, a top kill was performed to temporarily plug the well prior to a permanent cement capping. In these above ground applications, the top kill method proved effective because of the ease of accessibility to the well shaft and blowout preventer.[5]
Usage during the Deepwater Horizon oil spill
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On April 10, 2011, the oil platform Deepwater Horizon unexpectedly exploded, killing 11 workers and causing a massive oil spill into the Gulf of Mexico. The explosion caused a blowout of the well after the blowout preventer failed to operate as expected.[6]
After multiple efforts to plug the well failed, the top kill method was attempted. Starting on May 26, heavy drilling fluid weighing 13 pounds per gallon was pumped into valves of the blowout preventer. Over 7,000 barrels of drilling mud were pumped into the well. [7]
After multiple days, the top kill method was abandoned. The method was considered a failure for the application, as it did not plug the well’s flow.[8]
While the well was successfully plugged through use of other methods on July 15[9], multiple groups carried out a retroactive analysis of why the top kill method failed. In a report published in January 2011 by scientists at Lawrence Livermore National Laboratory, the potential reason of failure dealt with the counterflow instability of mixing fluids. Instead of maintaining a consistent fluid, the Kelvin-Helmholtz and Plateau-Rayleigh fluid instabilities caused the drilling fluid to separate into smaller particles, allowing the outgoing oil to flow through the drilling fluid and continue out of the well.
Lab experimentation provided results that suggested a shear-thickening liquid could successfully execute a top kill in a similar situation to the Deepwater Horizon incident. This is caused by strong elastic stresses that form in the fluid which suppress capillary instability and drop breakup entirely.[2]
References
edit- ^ a b c Rohrer, Finlo (27 May 2010). "What is a 'top kill'?". BBC. Retrieved 27 May 2010.
- ^ a b Paulo E. Arratia (2011). "Viewpoint: Complex fluids at work". Physics. 4 (9).
{{cite journal}}: Unknown parameter|month=ignored (help) - ^ Wellman, Robert Campbell (14 February 1999). ""Iraq and Kuwait: 1972, 1990, 1991, 1997." Earthshots: Satellite Images of Environmental Change". U.S. Geological Survey. http://earthshots.usgs.gov. Retrieved 27 July 2010.
{{cite web}}: External link in|publisher= - ^ Husain, T. (1995). Kuwaiti Oil Fires: Regional Environmental Perspectives. Oxford: BPC Wheatons Ltd. p. 68.
- ^ Brett Calnton (5 May 2010). "New tactic might seal leaking well sooner, BP CEO says". Houston Chronicle. Retrieved 29 May 2010.
- ^ Welch, William; Joyner, Chris (2010-05-25). "Memorial Services Honors 11 Dead Oil Rig Workers". USA Today. Retrieved 2010-05-26.
- ^ Jeff Crook (2010). "Stopping the spill". Engineering & Technology. 5 (13): 44–47. doi:10.1049/et.2010.1310.
{{cite journal}}: Unknown parameter|month=ignored (help) - ^ Kaufman, Leslie (29 May 2010). "BP Prepares to Take New Tack on Leak After 'Top Kill' Fails". The New York Times. Retrieved 25 November 2011.
- ^ "BP begins testing new oil well cap". Al Jazeera. 2010-07-15. Retrieved 2011-02-26.