News sources report that proper procedures were not followed in the hours and days before the Deepwater Horizon exploded in the Gulf of Mexico.

The attorney for a witness to April 20 Gulf Coast Oil Rig Explosion says BP and the owner of the drilling platform, Transocean Ltd., started to remove a mud barrier before a final cement plug was installed, a move industry experts say weakens control of the well in an emergency.  In the case of the Deepwater Horizon, a lawyer for a rig worker who survived the explosions, said the mud was being extracted from the riser before the top cement cap was in place, and a statement by cementing contractor Halliburton confirmed the top cap was not installed.  The witness saw mud being pumped out of the riser and onto boats that normally collect the mud in tanks. Another lawyer, who represents fishermen who witnessed the explosion and saw the mud being extracted beforehand.

When the explosion occurred, BP was attempting to seal off an exploratory well. The company had succeeded in tapping into a reservoir of oil, and it was capping the well so it could leave and set up more permanent operations to extract.  In order to properly cap a well, drillers rely on three lines of defense to protect themselves from an explosive blowout: a column of heavy mud in the well itself and in the drilling riser that runs up to the rig; at least two cement plugs that fit in the well with a column of mud between them; and a blowout preventer that is supposed to seal the well if the mud and plugs all fail.

If all of the mud had still been present, it would have helped push back against the gas burping up toward the rig, though it might not have held it back indefinitely.  When the gas got to the sea floor, the third defense – the blowout preventer — also failed, and it has continued to fail for weeks as unmanned submarines have tried to get it to engage.

But Halliburton said in a statement that it had completed pouring cement that lines the well 20 hours before the blowout. After that cement lining is done, the federal Minerals Management Service requires at least two prefabricated cement plugs to be placed at the bottom of the well and farther up, with mud packed in between. Halliburton’s official statement shows there was still one more cement plug to be inserted.

“Well operations had not yet reached the point requiring the placement of the final cement plug which would enable the planned temporary abandonment of the well, consistent with normal oilfield practice,” the Halliburton statement said.

Crew members were caught off-guard by a gas-bubble kick that spewed watered-down mud and an invisible plume of heavy gas onto the rig, igniting a fiery explosion that killed 11 crew members and doomed the rig.

Blowouts are not unprecedented, and are often caused by cementing failures. An MMS study found that half of 39 blowouts on offshore rigs from 1992 to 2006 were related to cement problems.

Even with the problems with cement seals and the weakening of the mud barrier, the blowout preventer, or BOP, a contraption built by Cameron International, still could have blocked the oil gusher. Unfortunately, those devices, too, have had documented troubles.