pretty much what happend.... and i drilled for a year or so and have worked on a rig for 4 years..... anyway heres what i think happend
when a rig has a blow out or a "Kick" its a simple deadly process your drilling a hole in the ground and you hit a gas pocket. if the mud is not weighted enough to hold down the gas the gas simple goes to the surface. there are many ways it could have happend... but i think the driller got lazy and didn't see the signs that you normaly see before a kick.. i've personally seen a kick and be on a rig when we took one it's not fun... but you have to have the crew trained to shut it in fast.