Blowout preventer

A blowout preventer (BOP) is a large valve that encases an oil well at surface. During drilling or well interventions, the valve may be closed if overpressure from an oil reservoir causes formation fluids such as oil and natural gas to back up within the wellbore and threaten the rig. By closing this valve (usually operated remotely via hydraulic actuators), the drilling crew can prevent explosive pressure release, thus regaining control of the reservoir pressure. Once this is accomplished, often the drilling mud pressure within the hole can be increased until enough fluid pressure is being placed on the reservoir, and the BOP can be opened for drilling to resume. The invention and use of BOPs resulted in the end of oil gushers, which were dangerous and costly.

Use

BOPs come in a variety of styles, sizes and pressure ratings. "Blind rams" are designed to close over an open wellbore. "Pipe rams" seal around tubular components in the well (drillpipe, casing, tubing, wireline or coiled tubing). "Shear-seal BOPs" are fitted with hardened steel shearing surfaces that can actually cut through drillpipe and toolstrings if all other barriers fail. Since BOPs are critically important to the safety of the crew, the drilling rig, and the wellbore itself, BOPs are inspected, tested and refurbished at regular intervals. BOP tests vary from daily function testing on critical wells to monthly or less frequent testing on wells thought to have low probability of well control problems. [cite web
url = http://www.glossary.oilfield.slb.com/Display.cfm?Term=blowout%20preventer
title = Schlumberger Oilfield Glossary
accessdate = 2007-01-18] Any of the above BOP's may be installed underwater. If this is the case, 2 hydraulic actuators are normally required.

Types

Blowout preventers come in two varieties -- ram and annular.

A ram blowout preventer utilizes two horizontally opposed hydraulic rams that either close around the drill string or shear through the drill string. It was invented by James Smither Abercrombie and Harry S. Cameron in 1922, and brought to market in 1924. [cite web
url = http://www.asme.org/Communities/History/Landmarks/First_RamType_Blowout.cfm
title = First Ram-Type Blowout Preventer (Engineering Landmark)
work = [http://www.asme.org/ ASME.org]
accessdate = 2007-01-18]

An annular blowout preventer (also known as a spherical blowout preventer) utilizes a hemispherical piece of rubber reinforced with steel. Unlike a ram BOP which closes with a sharp horizontal motion, an annular BOP closes around the drill string in a smooth simultaneous upward and inward motion. The geometry of this movement reduces internal stresses and friction between the BOP body and the sealing element, which translates into a longer field life with less maintenance. The annular design also operates with a much lower operating pressure, reducing the number of hydraulic accumulators necessary, thereby reducing cost and complexity. It was invented by Granville Sloan Knox in 1946; a U.S. patent for it was awarded in 1952. [cite web
url = http://www.oceanstaroec.com/fame/2003/Drilling.htm
title = Development of Offshore Drilling Equipment
work = [http://www.oceanstaroec.com/ OceanStar]
accessdate = 2007-01-18] [Patent US patent reference
number = 2609836
y=1952
m=09
d=09
inventor = Granville S. Knox
title = Control Head and Blowout Preventor]

Both types are usually used together, in oil well blow out preventer stacks.

References

ee also

*Wellhead
*Subsea
*Christmas or Xmas tree
*Oil well

External links

* [http://www.nov.com/Products.aspx?Puid=REDN_SV61se9oD&nodeId=DZ875VTUCTFEU0JSQBTR%2FSOL7O8%3D-BOBN_SV61SE9OD example of a ram blowout preventer]
* [http://www.nov.com/Products.aspx?Puid=gyENPbjm1se9oD&nodeId=4VGI6DUENQPJRRBXDHXYUZJIZUC%3D-GYENPBJM1SE9OD example of an annular blowout preventer]
* http://www.osha.gov/SLTC/etools/oilandgas/images/bop_stack.jpg
* http://www.osha.gov/SLTC/etools/oilandgas/drilling/wellcontrol.html
* http://www.asmenews.org/archives/backissues/july03/features/703oilwell.html