Blow out preventer(BOP)

A blowout preventer (BOP) is a large valve that can seal off at the surface wellhead a well being drilled or worked over. During drilling or well interventions, the valve may be closed if overpressure from an underground zone causes formation fluids such as oil or natural gas to enter the wellbore and threaten the rig. By closing this valve (usually operated remotely via hydraulic actuators), the drilling crew can prevent explosive pressure release, thus regaining control of the downhole pressure. Once this is accomplished, often the drilling mud density within the hole can be increased until adequate fluid pressure is being placed on the influx zone, and the BOP can be opened for operations to resume. The invention and use of BOPs were instrumental in the end of oil gushers, which were dangerous and costly.
BOPs come in a variety of styles, sizes and pressure ratings, and usually several individual units comprise a BOP Stack. Blind rams are designed to close an open wellbore. Pipe rams seal around tubular components in the well (drill pipe, casing, tubing, wire line or coiled tubing). Shear-seal BOPs are fitted with hardened steel shearing surfaces that can actually cut through drill pipe and tool strings, if all other barriers fail. Since BOPs are important for the safety of the crew, as well as the drilling rig and the wellbore itself, BOPs are regularly inspected, tested and refurbished. Tests vary from daily test of functions of critical wells to monthly or less frequent testing of wells with low likelihood of control problems.[1] Any of these BOPs may be installed underwater, normally with two hydraulic actuators.
[edit] Types