When oil drilling, installed at the wellhead casing head, used to control the high-pressure oil, gas, water blowout means. When high pressure oil and gas wells, wellhead blowout preventer can be closed (shut). From heavy mud into the drill pipe pressure, under which there are four shutter can replace the mud invasion disappointment, the well fluid column increased pressure to suppress the high-pressure oil and gas discharge.

Its sub-ordinary type BOP, BOP universal and rotary blowout preventer. Universal BOP can start in an emergency situation, to cope with any size drill and empty wells; the rotating BOP is achievable side spray while drilling operations. Often in deep drilling is in addition to two general BOP outside, coupled with the universal BOP, BOP rotation, so that a combination of three or four mounted on the wellhead.

Annular BOP ram type BOP usually equipped large gate, when the operation will be between the string and the wellbore to form a sealed annular space in the well under the circumstances string, plugging can be completed alone, but use several times to die, and does not allow the use of long-term shut-in.