"A SIMPLER PROTECTION...MUD"

 

A dead bird floats in oily water in Breton Sound about 10 miles southeast of Breton Island on Thursday.

From NOLA.com:

The investigation into what went wrong when the Deepwater Horizon exploded April 20 and started spilling millions of gallons of oil into the Gulf of Mexico is sure to find several engineering failures, from cement seals that didn't hold back a powerful gas bubble to a 450-ton, 40-foot-tall blowout preventer, a stack of metal valves and pistons that each failed to close off the well.

There was, however, a simpler protection against the disaster: mud. An attorney representing a witness says oil giant BP and the owner of the drilling platform, Switzerland-based 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.

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 its riches.

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.

In the case of the Deepwater Horizon, Scott Bickford, 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.

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.

The article doesn't mention the last-resort acoustic switch that was not installed on the Horizon.

The oil well spewing crude into the Gulf of Mexico didn't have a remote-control shut-off switch used in two other major oil-producing nations as last-resort protection against underwater spills.

The switch costs $500,000. The total cost of a rig like the Horizon can run over $100 million.