Blowout preventer (BOP)

A pressure-control valve installed at the top of a well. Depending on its design, a BOP can close around pipe, close an unobstructed bore, or shear specified tubulars and seal. Designs differ in size, pressure rating and closing mechanism. Terminology reference: SLB Energy Glossary, BOP — https://glossary.slb.com/terms/b/bop