[OT]Blowout.What I cant understand is how they didnt use the acoustic control all of those ultra deepwater rigs are equipped with. Typical, there is about 100 gallons of useable fluid stored on the BOP(Blowout Preventer, about 45' high, weighing about 200tons, latched onto the wellhead on the seabed.) at 3000 or 5000psi plus hydrostatic pressure(+.445psi per ft) ready for instant use. The BOP mounted bottles are filled with nitrogen, with a bladder or piston to seperate it from the fluid. The high pressure fluid is pumped in against the pressured nitrogen and the energized fluid is stored in that manner for emergency use.
It takes about 30 gallons to close the shear rams.
The shear rams are capable of shearing normal drill pipe and sealing off the hole to at least 10,000psi after the pipe is cut.
To operate, a transducer is dropped in the water and sends an acoustic signal down to the BOP. A transponder on the BOP picks up and processes the signal and using a BOP mounted battery/processor pack, opens a small control fluid solenoid operated hydraulic valve. The control fluid is sourced from the stored fluid. That control fluid then applies operating force to a much bigger 1" ID valve and bang,the 1" valve unloads the stored pressure onto the back of the shear rams and the shear rams are slammed shut with sufficient force to close off the well and cut the pipe.
Acoustic systems are designed for use in exactly this type of situation where all normal control from the rig is lost. The problem is a lot of rigs store these mobile control units close to the well where they are unaccessable once things get hot.
If the gas pushed the casing up into the BOP, then that is another matter. Not all BOPs can shear casing.
Once the rig came to rest on the BOP the acoustic signal would not get through.
All deepwater BOPs also have ROV intervention ports, there the ROV(robot submarine) can plug into the intervention port and function a ram.
All of these seperate control systems run through shuttle valves, which, when the flow is applied to the side of the valve, the slug in the valve shifts across to block off the other redundant controls. They are simple systems and should work.
Before the BOP is run to bottom all of this is tested, and once it is run to bottom is tested again. The rig cannot proceed with drilling till all BOP controls have been tested and verified.
Maybe they should have let it burn, but it probably would have sunk in the end and with that heat, nobody was going to get near the rig and all normal controls would have already been destroyed.
In situations like this it is often hard to find out for sure what mistakes were made. When the Lexington burned in the 1980s most of the decision makers perished.
