Two Oil Firms Link Rig Blast to 'Plug' - WSJ.com

Two Oil Firms Link Rig Blast to 'Plug' - WSJ.com

At this point it is common practice to pour wet cement down into the pipe. The wet cement, which is heavier than the drilling mud, sinks down through the drilling mud and then hardens into a plug thousands of feet down in the well.

The mud then is removed and displaced by seawater; the hardened cement plug holds back any underground gas.

In this case, a decision was made, shortly before the explosion, to perform the remaining tasks in reverse order, according to the expected Senate testimony of Mr. Probert, the Halliburton executive.