Reply #19: Okay - I was wrong

[underpants]

According to the account he has pieced together, a group of BP executives were on board the Deepwater Horizon rig celebrating the project's safety record while, far below, the exploration well was being converted for oil production.

The workers set and then tested a cement seal at the bottom of the well, he believes, but - as they reduced the pressure in the drill column and attempted to set a second seal below the sea floor - a chemical reaction caused by the setting cement created heat.

That heat converted a pocket of methane crystals into a bubble of compressed gas which grew as it rose up the drill column.

http://www.telegraph.co.uk/finance/newsbysector/energy/oilandgas/7696596/BP-oil-disaster-how-a-deadly-methane-bubble-triggered-explosion.html