Oakes, the space between the drill pipe and the casing is called the annulus. The annulars and all of the rams except the shear rams close/seal off the annulus.
For any who dont know, the well casing in the ground/seabed is attached to a heavy duty wellhead which sticks up from the seabed a few meters. The BOP latches with hydraulics to the wellhead with a 15,000psi seal. The riser which is the main tube to take circulation back to the rig is attached to the top of the BOP. The inside of all those components form a single pipe. Outside the BOP is seawater. It is not possible to go around it, everything goes through it.
You are correct that the gas influx from the well possibly flowed up through the bad cement plug, then up the annulus around the drill pipe, but through the BOP to stop and build up beneath the closed annular at the top of the BOP. There are at least 4 points below the annular in the BOP where wellbore pressure can be monitored.
In saying that remember we dont know exactly what happened. I am sure Transocean had a very competent crew on tour, but in a pressure situation like that it only takes a small malfunction of equipment or a bad choice under extreme pressure for things to go very wrong. That so many perished tells me they all stayed to fight it.
There are ROV intervention stabs on a few of those functions and it should be an easy job to go down there with an ROV, plug in and close a function. In this case the shear rams I think.
For anyone interested in what an annular is.
The annular is a doughnut shaped block of rubber or synthetic with radial steel segments moulded into the rubber facing towards the hole center. A doughnut shaped hydraulic piston, with a wedge profile is forced up with its wedge profile driving up behind the rubber doughnut shaped element. The action of the round wedge being driven up behind and below the round rubber element, forces the rubber and steel segments in towards the center till they are tight against the pipe, with the steel segments almost touching each other. On that rig I would guess it is a 10,000psi wellbore pressure annular. Hydraulic perating pressure about 1500psi. That big doughnut shaped piston has a huge piston surface area and 1500psi operating pressure represents a great closing force. Under that closing force the rubber flows like fluid. Of course the piston and element is encased in a heavy steel body.
Normally you would not kill a well oil or gas kick on an annular. An annular will close on anything and even open hole. An annulars main use is to close on the pipe if you suspect there is a formation fluid/gas influx while drilling. Once drilling is stopped and the annular is closed, a choke line is opened up below to monitor any pressure build up in the well below the annular. If a pressure build up is detected, the pipe can be stripped through the annular to locate the tooljoint, then a ram (two solid steel blocks with front seals and top seals, one enters from each side of the bore)with a 5" drill pipe profile closed onto the pipe and the tooljoint(larger collar where two drill pipe are screwed together) is hung off on top of the ram. Rams are more reliable and in this case rated working pressure of 15,000psi and can support the drill string weight. Well killing operations start in earnest once the drill pipe is securely in the pipe rams.
News 
Market Data 
Discover 
