BOPs, or “blowout preventers” are valves that can seal off the wellhead, when it needs maintenance, or in case of an emergency. If pressure from underground, or undersea reaches a dangerous level, potentially causing fluids and natural gas to enter the wellbore, the valve closes, to protect the rig. The invention of this method has been useful in ending oil gushers, which were at one time, capped.
The BOP works by hydraulic actuators, which are monitored by the drilling crew, and operated remotely. If the well needs to be shut off due to fluids or gas in the line, drilling mud density within the hole is increased until the pressure is stabilized and the well can reopen.
In the case of offshore oil rigs, pressure readings are monitored both on the rig and at an onshore facility to determine if the preventers are needed, if they are operational, and if manual activation is required. In cases where manual activation hasn’t been used, preventers are equipped with a “Deadman” control that automatically operates the equipment when needed.
There are two types of BOPs, ram and annular, and both are most commonly used together in oil well stacks, which are the combinations of several blowout preventers stacked together.
The ram unit uses two hydraulic rams that can close around the oil string or actually cut through the drill string and seal off the wellbore when necessary. The ram was a creation of James Smither Abercrrombie and Harry S. Cameron back in 1922.
The annular, or spherical BOP uses a piece of rubber reinforced with steel. The annular BOP closes around the drill string, reducing internal stress and friction between the BOP and the sealing element. This was invented in 1946 by Granville Sloan Knox.
Blowout preventers come in many styles, sizes, makes and pressure ratings, determined by the size of the operation, the desired function and the location where they are to be installed. Since their function is crucial to the safety of oil operations, they are regularly tested, maintained, and checked for defects. It is normal for monthly or weekly tests to be run on these safety mechanisms, as well as daily checks.
Blowout preventers are definitely one of, if not the most, important safety feature on an oil rig, however, in the past, there have been problems. There is an ongoing technological push to improve on these devices to make them even more reliable and less prone to breakdown.
http://www.osha.gov/SLTC/etools/oilandgas/drilling/wellcontrol.html
