Blow Out Preventer
A Blow Out Preventer commonly known as BOP is a large valve placed on top of a well. As the name suggests, BOP is used to prevent a blowout in a well.
The conventional process of drilling a well maintains the pressure (force per unit area) inside the wellbore higher than the formation pressure. The difference between the hydrostatic pressure in the well and the fluid pressure in the formation being drilled is called overbalance. Overbalance is considered the 'Primary Barrier' in a well.
If for any reason, this primary barrier fails and the hydrostatic pressure in the well falls below the formation pressure, the formation fluid will start entering the well. If this situation is allowed to continue, the heavier drilling fluid will be completely displaced by the formation fluid, which will be gushing out of the well with high force due to pressure from the formation. This situation is called a blowout.
Blow-Out Preventers are designed to close the well and contain the pressure in such scenarios. BOP makes it possible not only to avoid a blow-out but also to circulate the kick out of the well by displacing the well with kill weight fluid. Different types of BOPs are placed on top of the well in the form of a stack. BOPs have different pressure ratings depending on the type of well.