The second line of defense for the workers and the well to prevent a blowout is the group of equipment called blow out preventer. BOPs and associated valves are installed on top of the casing head before drilling ahead after rigging up. These high-pressure safety valves and associated equipment are designed to shut off the well hole and prevent the escape of the underground fluids and prevent a blowout from occurring.
After installation, the BOP and associated valves are pressure tested to ensure integrity and proper operations.
The BOP and associated equipment consist of:
How the blow out operates
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 (drill pipe, casing or tubing).
Others are fitted with hardened steel shearing surfaces that can actually cut through drill pipe.
Because 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.
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