A blowout preventer valve (BOP) is a safety valve that is mounted on top of the surface wellhead that is being bored for oil or natural gas. The valve is usualy closed to prevent the pressurised underground fluids from flowing into the bore and destroying the drilling rigs; thus through hydrolics the crew has total control over the wellbore. To restabalise fluid flow, the drilling mud density is increased to stabalise the pressure on the influx zone, thus regaining control of the well.
The BOP is usually activated via five methods:
a) Electrical activation.
b) Via pressure gradients.
c) Automatic activation, depending on the flow sensors.
d) Underwater, external valve motion.
e) Acoustic activation through a transducer.
Blow out preventors are usually installed in series over the well head. However, there are two types of BOPs; they are:
a) Rams (Utilizes two horizontally opposed hydraulic rams)
Blind rams are designed to seal of a well when in the closed mode, thus it is a safe option for covering tubless wells. While Pipe rams are installed on drilling pipes.
b) Annular (Utilizes reinforced steel and a hemispherical rubber molding)
The number of hydrolic accumulators is reduced in comparison to the rams. This is due to the ability of annular BOPs to opperate at much lower pressure then their ram counterparts. Thus the cost and duration of the installation and the oil siphoning process is greatly reduced.
Failure of BOPs can often be catastrophic, as high pressure gushers reach the surface and ignite, thus lighting the enrire oil platform; as had happened at the Deepwater Horizonin 2010, being the latest north American ecological disaster that had threatened the entire south eastern coast of the USA. Like on the Deepwater Horizon lack of proper maintenance had accumulatd multiple faults in the blow out preventer. Thus when oil pressure increased beyond the endurance of the BOP the entire system blew. The investigation had concluded that due to a faulty/flat battery the BOP was not able to activate in an emergency procedure to shut of the oil flow, to add to this the hydrolics accompanying the electrical equipment were not strong enough to initiate a manual shut off.
The poor quality blowout preventer could simply not withstand the pressures and was blown apart by the enormous pressure of the oil. Therefore, there is a reason why BOPs are checked weekly in isolated rigs and platforms to ensure a safe working environment for the crew and the surrounding environment. Hence, oil companys are advised to spend considerable amount of money on research and development of blowout valvues; some of which end up costing upwards of half a million dollars.