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There seems to be a lot of confusion about the process involved in this "top kill" process.
The blowout preventer has various lines attached to allow the well to be worked in the event that the blowout preventer activates and seals the wellhead. In a blowout, the BOP squeezes down on the drill pipe (extremely heavy-wall tubing tipped by the drill bit). Should this fail, the BOP has a ram capable of cutting through the steel alloy drill pipe, sealing the well like a monstrous hardware store gate valve. There is no conclusive evidence as to why this final failsafe failed, but some believe that the cutoff ram closed on a joint (drill pipe commonly runs 31 feet long, with massive threaded ends), which is significantly stronger and effectively impossible to cut. Whatever the case, best estimate is that there are approximately 90 joints of drill pipe still in the well (~2800 feet). The drill pipe runs through drill casing, which in this case is approximately one half inch larger in inside diameter than the large joints in the drill pipe in outside diameter. This "annulus" means a 1/4 inch gap around the drill pipe joint.
The top kill requires that the operators pump high viscosity drilling mud (primarily cat litter mixed with water to the viscosity, in this case, of peanut butter) through the service lines into the casing. The flow rate must overcome the outflow of oil through the disable BOB sufficiently to begin flowing down into the drill casing. Then, while gushing out through through the BOP, the flow must also overcome the downhole pressure so that mud can be forced through 90 narrow cracks between the drill pipe joints and the drill casing. Sufficient mud has to fill the casing such that the weight of the mud column overcomes the formation pressure which may exceed 100,000 psi. It was hoped that by tossing trash into the mud (junk shot), the leaky blowout preventer could be plugged sufficiently to allow mud to be forced down hole. In short, the kill requires pumping mud into the BOP faster than it could squirt out of the top to such an extreme that mud flows not only out the top, but out the bottom, into the well, against extreme pressure. Through a couple of three inch lines. Then through narrow gaps between drill pipe and drill casing. Ninety of them.
The problem is that if you just add more pumps and more power, eventually, you will explode the BOP or pump it off the surface pipe, which at the moment is the only thing holding the oil back.
I've seen something like this done with gangs of turbine-powered monster pumps on dry land. That was indescribable. The heat and sound was overwhelming. The ground quivered with the forces involved. In that case, the BOP held. This kill is an order of magnitude more difficult.
BP's claim of a 60-70% probability of success was propaganda or opium dreams.
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