Crucially, both the Gulf and Caspian Sea blow-outs had the same identical cause: the failure of the cement “plug”.
To prevent blow-outs, drilled wells must be capped with cement. BP insisted on lacing its cement with nitrogen gas – the same stuff used in laughing gas – because it speeds up drying.
Time is money, and mixing some nitrogen gas into the cement saves a lot of money.
However, because BP’s penny-pinching method is so damn dangerous, they are nearly alone in using it in deep, high-pressure offshore wells.
The reason: nitrogen gas can create gaps in the cement, allow methane gas to go up the borehole, fill the drilling platform with explosive gas – and boom, you’re dead.
So, when its Caspian Sea rig blew out in 2008, rather than change its ways, BP simply covered it up.