What is a blowout preventer?
The Blowout Preventer, or BOP, is safety equipment designed to prevent uncontrolled flow of formation fluids during drilling and completion operations. During drilling, mud is pumped down the drill string to lubricate and cool the bit, and provide equalizing pressure in the well. If the well’s hydro-static pressure falls below the formation’s pressure, a kick can occur, allowing gas, oil, and salt water fluids to enter the well bore.
During a kick, these pressurized, combustible, hydro-carbons can be pushed up the well bore to the surface, where they may potentially blow out the well and ignite. The BOP has the capability to control this flow by sealing off the well bore in several ways.
The Blowout Preventer is comprised of four main components, stacked one upon another. They are the annular preventer, blind ram, blind shear ram, and the pipe ram. There can be many different configurations, sizes and pressure ratings, dependent on well design, formation pressures, and areas of use. The BOP is attached to the steel casing that is cemented around the well bore. The drill string is suspended through the center of the well bore. This is the rotating pipe to which the drill bit is attached.
The first BOP component is the pipe ram. During a kick, this ram is activated and creates a seal between the well bore and the outside of the drill string. The next component is the blind shear ram. If a kick occurs, it may become necessary to sacrifice the drill string to stop the flow of material inside of the well bore. The blind shear ram performs this function by cutting, or shearing the drill string, and sealing the well bore. The blind ram is used to seal the well bore when there is no drill string in the well. The annular preventer is a device that can seal around any object in the well bore, or upon itself. It is designed to create a seal, with or without the drill string present.
These multiple components provide redundancy, and are controlled by a device called the accumulator. This unit can be operated remotely, using a panel located on the rig floor, or by personnel on the ground, using duplicate controls on the accumulator itself.
The second line of defense for the workers and the well to prevent a blowout is the group of equipment called blowout preventers (BOPs). BOPs and associated valves are installed on top of the casing head before drilling ahead after rigging up. These high-pressure safety valves and associated equipment are designed to shut off the well hole and prevent the escape of the underground fluids and prevent a blowout from occurring. After installation, the BOP and associated valves are pressure tested to ensure integrity and proper operations.
The BOP and associated equipment consist of:
A BOP installation could consist of both annular and ram-type BOPs assembled into a stack. Also, there can be a kill line valve and a choke line valve. The choke line valve is used to redirect the mud from the well bore to the choke manifold during a kick. The kill line valve is used to direct drilling fluid to the BOP during a kick.
Ram-type BOPs have rubber faced steel rams that come together with great force to seal the wellbore. Usually two or more ram-type BOP’s are mounted in the BOP stack.
A choke manifold is a system of valves used to circulate out a kick and to circulate mud in of the proper weight. This device responds automatically to a kick and can prevent a blowout if properly installed and maintained.
The BOP control system, called an accumulator, provides the energy to operate the blowout preventers.
This system of consists of:
Compressed gas bottles, Regulator valves, Pumps, Hydraulic reservoir, Control manifold, and Control valves.
Source: OSHA – osha.gov
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