Deepwater Horizon - Transocean Oil Rig Fire

A couple interesting comments made by Kent Wells during the briefing on the 17th…

“…[I]you’ll see we’ve got some bubbles coming from a valve that’s on the 36 inch casing.
…This is quite normal… It’s more likely [B]nitrogen[/B] or it could be biodegradable methane or something like that.[/I]”

Nitrogen? Anyone know if they used nitrified cement on the 28" and/or 22" casings? Otherwise this is bollocks.

“…[I]And when – as I talked about as the well is cooling down – as the well is cooling down that’s probably what caused those bubbles there[/I].”

Correct me if I am wrong here, but when a volume of gas/liquid cools down then its pressure decreases.
If there were no bubbles before then there should be even less of a possiblity of bubbles occuring now if the wellhead/BOP etc are cooling down. (Or looking at it a different way, if there were bubbles before they shut in then cooling would reduce the quantity of those bubbles).

The only reason I know of bubbles to suddenly appear is due to a pressure increase from somewhere else affecting the void spaces behind those valves.