Geology And Geophysics

What is a Blowout Preventer



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By now, most people who watch or read the news have a basic idea of what a blowout preventer is.  Ask anyone on the street and answers will probably sound something like, “It’s a valve that malfunctioned or wasn’t shut right and that’s why the oil is leaking into the Gulf.”  That’s about right, in layman’s terms.

From the Oilfield Glossary:

A blowout preventer is “a large valve at the top of a well that may be closed if the drilling crew loses control of formation fluids.”

Kinds of Blowout Preventers

Ram Blowout Preventer (BOP):  There are three kinds of ram BOPS – blind, pipe and shear.  Blind rams and pipe rams seal a well when closed.  Blind rams are used on wells with no pipe or tubing.  Pipe rams are used on wells with a drill pipe.  The ram BOP was invented by James Smither Abercrombie and Harry S. Cameron in 1922.

A spherical BOP uses a curved piece of steel-reinforced rubber to close around the drill pipe in a smooth upward and inward motion.  This kind of movement reduces stress to the BOP, which gives it a longer life and requires less maintenance. It was invented by Granville Sloan Knox in 1946.

In most cases several blowout preventers are installed on top of the well creating a BOP stack.  A spherical BOP is installed on top with at least one blind ram BOP and one pipe ram BOP below.

By closing the BOP, the drill crew can take back control of the reservoir, and actions can be taken to increase the mud density until it is possible to open the BOP and maintain pressure control of the formation. Since blowout preventers are critical to the safety of the crew, the rig and the well itself, they are inspected, tested and renovate regularly.  How often the BOPs are inspected and tested is determined by the kind of well it is installed on and legal requirements or local practice in that area.  Some BOPs are tested every day, especially on wells in risky locations.  Other BOPs, such as those installed on wells thought to have a low risk of problems, are tested monthly or less.

Nearly a month after the Deepwater Horizon exploded, killing eleven and spewing crude oil into the Gulf of Mexico, a special House energy panel investigation has determined that the blowout preventer on this well had multiple faults that contributed to it failing.  Though BP said the BOP was “fail-safe”, the investigation found that the BOP had a dead-battery in its control pod, leaks in its hydraulic system and a cutting tool that wasn’t strong enough to cut through the joints in the well pipe.  The BOP on the Deepwater Horizon would never have been able to do what it was designed to do in the condition it was in, effectively making the Gulf oil spill not only an accident waiting to happen but a catastrophe in the making.

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