Blowout preventer Definition
1. one of several valves installed at the wellhead to prevent the escape of pressure either in the annular space between the casing and drill pipe or in open hole (i.e., hole with no drill pipe) during drilling completion operations. blowout preventers on land rigs are located beneath the rig at the land’s surface; on jackup or platform rigs, at the water’s surface; and on floating offshore rigs, on the seafloor.
2. a large valve at the top of a well that may be closed if the drilling crew loses control of formation fluids. by closing this valve (usually operated remotely via hydraulic actuators), the drilling crew usually regains control of the reservoir, and procedures can then be initiated to increase the mud density until it is possible to open the bop and retain pressure control of the formation. bops come in a variety of styles, sizes and pressure ratings. some can effectively close over an open wellbore, some are designed to seal around tubular components in the well (drillpipe, casing or tubing) and others are fitted with hardened steel shearing surfaces that can actually cut through drillpipe. since bops are critically important to the safety of the crew, the rig and the wellbore itself, bops are inspected, tested and refurbished at regular intervals determined by a combination of risk assessment, local practice, well type and legal requirements. bop tests vary from daily function testing on critical wells to monthly or less frequent testing on wells thought to have low probability of well control problems.
Related Oil & Gas Terms
Openhole
The uncased portion of a well. all wells, at least when first drilled, have openhole sections that the well planner must contend with. prior to running casing, the well planner must consider how the drilled rock will react to drilling fluids, pressures and mechanical actions over time. the strength of the formation must also be...
Bullheading
1. forcing gas back into a formation by pumping into the annulus from the surface. 2. any pumping procedure in which fluid is pumped into the well against pressure. 3. to forcibly pump fluids into a formation, usually formation fluids that have entered the wellbore during a well control event. though bullheading is intrinsically risky, it is...
Downhole safety valve
A downhole device that isolates wellbore pressure and fluids in the event of an emergency or catastrophic failure of surface equipment. the control systems associated with safety valves are generally set in a fail-safe mode, such that any interruption or malfunction of the system will result in the safety valve closing to render the well safe. downhole...
Mobile offshore drilling unit
A drilling rig that is used exclusively to drill offshore exploration and development wells and that floats upon the surface of the water when being moved from one drill site to another. it may or may not float once drilling begins. two basic types of mobile offshore drilling units are used to drill most offshore...
Drill stem test (dst)
The conventional method of formation testing. the basic drill stem test tool consists of a packer or packers, valve or ports that may be opened and closed from the surface, and two or more pressure-recording devices. the tool is lowered on the drill string to the zone to be tested. the packer or packers are...
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