Geology And Geophysics

What is a Blowout Preventer

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"What is a Blowout Preventer"
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BOP – Blow Out Preventer did not work on British Petroleum’s rig, Deepwater Horizon.  Now comes the let’s name who is to blame game.  What happened to the blowout preventer on the rig?  The fail-safe equipment is the last defense to stop a gushing pipe with up to one million pounds of force.

Here is a look at the BOP and how it works.

The BOP is enormous – about three stories high – made out of 640,000 pounds of valves and hydraulic pistons encased in steel.  It is the first equipment on the ocean floor.  It begins on the sea floor and extends to the top of the well.  It can detect and plug the well, if an emergency should arise.   The pressure of the drilling mud keeps the oil in place.  The metal drill bit breaks up  the rock and the pressure of the drilling fluid helps pull out the bits of rock.  The mud lubricates the bit.  The mud pressure circulating through the drill holds the oil in the well. When something goes wrong, and there is too much pressure, the mud forces the mud back into the wellbore  It then  blows up in a geyser that carries the mud and oil into the air.  A blowout of the rig is usually the result of a natural gas bubble forcing its way up through the pipe.

There are three types of valves used in BOP.  The whole BOP installation is the “BOP Stack.”  The following are valves and functions of the BOP stack.

One valve is a “ram”.   It is a certain diameter with rubber faced steel rams that ram (hence the name) into each other with massive force.  This seals the wellbore.

The second valve is an “annular” valve mounted at the top of the stack, above the ram preventer and designed to form a seal in the space between the pipe and wellbore. The process of cementing helps keep oil and natural gas from discharging by filling gaps between the outside well pipe and the holebore in the ocean floor.  The cement plugs wells after the well becomes dry.

The third type is a series of valves called a “choke manifold.”  It responds to a kick by circulating the mud when the preventers close to control the pressure.

The Interior Department’s branch, U.S. Minerals Management Services, reported that there have been about 14 accidents since 2005.  Transocean, the owner of the destroyed rig, pointed out that the BOP was unreliable and exceedingly costly for offshore drilling contractors.

The BOP on the Deepwater Horizon used all three of the BOP valves.  Each is an individual Blow Out Preventer. 

What went wrong on the Deepwater Horizon will take time to discover.  However, this massive catastrophe must be avoided in the future.

More about this author: Nan C Avery

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