Geology And Geophysics

What is a Blowout Preventer

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"What is a Blowout Preventer"
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Many Question the Effective Safety of the Devices.

If you haven’t heard the term “blowout” over the last few days then you haven’t been reading the daily news or watching the events unfold in the Gulf of Mexico.  The British Petroleum (BP) operated deepwater oil rig that sits 50 miles off of the Louisiana coast line has had one of the worst blowout accidents since a similar one occurred in the Gulf back in 1979.  The affects of the blowout destroyed the rig, sinking it and snapping the line near the floor of the sea 5000 feet below.  Currently the rate of flow is estimated to be 25,000 barrels a day.

The blowout occurred because the Blowout Preventer – a BOP – didn’t function properly to contain the effects of the blowout.  The BOP is a vital piece of fail safe equipment designed to attach at critical locations on an oil rig’s well bore to prevent the sudden rapid escape of oil, gaseous elements, soil sediments and sea water while the drilling or production process is in operation.  In a nutshell they are designed to manually or automatically close off a well bore to prevent the blowout of these elements under the right conditions.

There is a gap, referred to as the annulus, between drilling string or tubing (connected pipes to burrow the hole for oil and gas) and the casing which make up a well bore. (See diagram here).  When there is a blowout, air and liquids will escape up that gap back to the top of the well bore where men and machinery are at work.  The released pressure through the top of the well bore at the platform is a threat in itself if you are anywhere near the opening when it exits.  But, as happened on the BP rig last April 20th, if there are ignitable liquids or gas escaping with this blow out, any flame or electrical charge that it comes into contact with creates an explosion.  The BOP is in place to prevent such disasters.

The deeper the well bore the more necessary it becomes to have a functional, tested Blow out Preventer, and properly installed at locations to prevent disasters.  For deepwater drilling, best safety practices require that a BOP be installed at the sea floor that can be remotely controlled from the surface.  Regular inspections of this device are essential to insure the mechanism doesn’t become defective and repairs or replacement should also occur at routine intervals.  BP is under investigation for failure to follow the safety procedures for their BOP that became disabled.

The earliest BOPs were developed in the Texas oil fields back in 1922.  Before this invention came along the oil that gushed from drilling rigs could not be capped until the underground pressure had released large quantities of the black crude naturally.  The original BOP was a ram-style BOP which simply had valves to shut the opening of a well bore.  Later designs would seal off the cavities (annulus) between the drill pipe and the casing, called an Annular or pipe ram BOP and the most recent innovation called a shear ram BOP actually has shears to cut through the well bore and seal it.

A device known as a choke manifold may also be an inherent part of some BOPs.  The choke manifold is an arrangement of pipes and valves at the top of the well bore that controls “drilling mud” in the line to maintain pressure and prevent blowouts.  Each style of BOP could be attached separately or as part of a single unit whose design followed the contours of a “christmas tree”, a name that has been used for this part in the industry for years. 

However, the effective success rate of BOPs has been less than stellar.  Under the extreme conditions of deepwater drilling the fail safe devices have had a myriad of problems.  A recent AP story revealed several shortcomings for this essential item of last resort to protect men and property.  Reports from the government agency responsible for monitoring U.S. mining and oil drilling practices, the Mineral Management Services, have revealed BOPs “have failed or otherwise played a role in at least 14 accidents, mostly since 2005.” 

Testing in the 1990’s by MMS found that BOP failures were more common than the oil industry was independently stating.  There were “117 blowout preventer failures at deepwater rigs [in 1998]. These breakdowns created 3,638 hours of lost time …”   Routine inspections by rig operators were not occurring and the MMS itself was lax in it regulatory oversight of the industry. (Blowout preventers known to fail, by Jeff Donn and Seth Borenstein, AP, 5/9/10)

The units vary in size and price.  Some can be as big as a “double-decker bus” and cost as much as $800,000.  In fact this has been raised as a point of concern where costs incurred by the oil companies to supply and install proper BOP safe guards and the subsequent expense to maintain and inspect them over time resulted in low levels of safety on job sites.  The ensuing investigation with the oil rig catastrophe in the Gulf of Mexico with BP’s platform may reveal that corners have not only been cut here to maximize profits, but throughout the U.S. oil industry over the preceding years.


Invention of ram-type BOP

The Oil Drum

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