A blowout preventer (BOP) is a safety device that sits on top of well when the well is being drilled. It is used to prevent blowouts which is when there is an uncontrolled release of gas or fluids from the well. The BOP is also used to help control the well when there are pressure spikes or 'kicks'. The BOP can be operated remotely and when it is closed it creates a pressure tight seal that traps the gas or fluids in the well preventing them from escaping.
There are two categories of BOP's:
- Annular Blowout Preventer
- RAM Blowout Preventer.
Annular BOP's are located at the top of the BOP stack. They can close around the string string, casing, or tubing. Annular BOP's are effective at maintaining a seal even while the well is being drilled. However, Annular BOP's are not as effective at fully closing off a well as RAM BOP's.
RAM BOP's use opposing steel plungers which slam together when the valve is closed. There are four (4) types of RAM BOP's; Pipe rams, Blind rams, Shear rams, and Blind Shear rams. Depending on the type, the RAM BOP can close around the drill pipe, close off the well that has no drill pipe, or shear off the drill pipe and close the well.
A typical setup may include one or two Annular BOP's at the top of the BOP stack with multiple RAM BOP's below the Annular BOP. The Annular BOP is closed first. If it fails the RAM BOP's are closed. This provides redundant safety mechanisms to prevent and control well blowouts.