Blowout preventer
A blowout preventer (BOP) (pronounced B-O-P)[1] is a specialized valve or similar mechanical device, used to seal, control and monitor oil and gas wells to prevent blowouts, the uncontrolled release of crude oil or natural gas from a well.
The earliest blowout preventers; Regan Type K Annulars were used, beginning in the 1930s to cope with extreme erratic pressures and uncontrolled flow (formation kick) emanating from a well reservoir during drilling.
Multiple blowout preventers of the same type are frequently provided for redundancy, an important factor in the effectiveness of fail-safe devices.
This is less desirable because of the higher surface pressures likely needed and the fact that much of the mud originally in the annulus must be forced into receptive formations in the open hole section beneath the deepest casing shoe.
Thus a key focus in the technological development of BOPs over the last two decades has been limiting their footprint and weight while simultaneously increasing safe operating capacity.
[3] A ram-type BOP is similar in operation to a gate valve, but uses a pair of opposing steel plungers, rams.
Such screw jack type operation provided enough mechanical advantage for rams to overcome downhole pressures and seal the wellbore annulus.
Relatively rapid actuation and remote control were facilitated, and hydraulic rams were well-suited to high pressure wells.
Because BOPs are depended on for safety and reliability, efforts to minimize the complexity of the devices are still employed to ensure longevity.
As a result, despite the ever-increasing demands placed on them, state of the art ram BOPs are conceptually the same as the first effective models, and resemble those units in many ways.
Typical ram actuator assemblies (operator systems) are secured to the BOP housing by removable bonnets.
Shear-type ram BOPs require the greatest closing force in order to cut through tubing occupying the wellbore.
[citation needed] Technological development of ram BOPs has been directed towards deeper and higher pressure wells, greater reliability, reduced maintenance, facilitated replacement of components, facilitated ROV intervention, reduced hydraulic fluid consumption, and improved connectors, packers, seals, locks and rams.
[citation needed] The spherical annular blowout preventer was invented by Granville Sloan Knox in 1946; a U.S. patent for it was awarded in 1952.
When the piston is actuated, its upward thrust forces the packing unit to constrict, like a sphincter, sealing the annulus or openhole.
In deeper offshore operations with the wellhead just above the mudline on the sea floor, there are five primary ways by which a BOP can be controlled.
The EDS is also intended to automatically trigger the deadman switch, which closes the BOP, kill and choke valves.
[citation needed] Pumps on the rig normally deliver pressure to the blowout preventer stack through hydraulic lines.
[citation needed] During the Deepwater Horizon drilling rig explosion incident on April 20, 2010, the blowout preventer should have been activated automatically, cutting the drillstring and sealing the well to preclude a blowout and subsequent oil spill in the Gulf of Mexico, but it failed to fully engage.
Whether the valves closed automatically during the explosion or were shut manually by remotely operated vehicle work is unknown.
[9] A statement released by Congressman Bart Stupak revealed that, among other issues, the emergency disconnect system (EDS) did not function as intended and may have malfunctioned due to the explosion on the Deepwater Horizon.
[10] The permit for the Macondo Prospect by the Minerals Management Service in 2009 did not require redundant acoustic control means.
[11] Insofar as the BOPs could not be closed successfully by underwater manipulation (ROV Intervention), pending results of a complete investigation, it is uncertain whether this omission was a factor in the blowout.
Documents discussed during congressional hearings June 17, 2010, suggested that a battery in the device's control pod was flat and that the rig's owner, Transocean, may have "modified" Cameron's equipment for the Macondo site (including incorrectly routing hydraulic pressure to a stack test valve instead of a pipe ram BOP) which increased the risk of BOP failure, in spite of warnings from their contractor to that effect.
Another hypothesis was that a junction in the drilling pipe may have been positioned in the BOP stack in such a way that its shear rams had an insurmountable thickness of material to cut through.
The DNV final report indicated that the second tube was the segment of the drill string that was ejected after being cut by the blow out preventer shears.
Based on BP's video feeds of the operation the sealing cap assembly, called Top Hat 10, included a stack of three blind shear ram BOPs manufactured by Hydril (a GE Oil & Gas company), one of Cameron's chief competitors.
[14] On September 3, 2010, at 1:20 p.m. CDT the 300 ton failed blowout preventer was removed from the well and began being slowly lifted to the surface.
[15] The failed blowout preventer was taken to a NASA facility in Louisiana for examination[15] by Det Norske Veritas (DNV).
The upper section of the blow out preventer failed to separate as designed due to numerous oil leaks compromising hydraulic actuator operation, and this had to be cut free during recovery.
