[wideminded]

BP engaged Halliburton to seal the well so that they could transition to production from drilling. This process can't be done with mud in the drill pipe, so they had to either push it down or get it out.

I'm in no way an expert on oil well drilling, but I did do a little Internet research on the methods of installing "balanced plugs" in oil wells. It looked to me like it is often standard procedure to install a plug with the mud still in place.

For instance, if the mud is being circulated down through a central pipe and out through the "annulus", they only have to insert a measured slug of cement in the mud stream, and knowing all the volumes, stop the stream when the cement is just at the bottom and is balanced in the central pipe and annulus. Then they withdraw the central pipe and let the cement cure.

[Cold Heat]

Not sure what method they used to seal or what else they may have sealed via Halliburton. I have worked only shallow water rigs or 500foot and less. This well extends more than 12000 feet below the ocean floor in addition to being a mile deep. The pressures dictate methods for the most part.

I think what happened was that a previously undetected reservoir of nat gas found it's way to the well and began expanding, pushing the oil and anything else in it's way out to the surface. The well went out of spec. They did not catch it in time and likely could not have stopped it anyway. Then the BOP failed and that was that.