Oil rig blast caused by gas hydrates, Berkeley professor believes

A UC Berkeley professor who is conducting an informal assessment of the Deepwater Horizon wellhead blast said Tuesday that BP documents leaked to him indicate that contaminants in cement encasing the well were the initial cause of the explosion that led to the ongoing oil spill in the Gulf of Mexico.

Robert Bea, a UC Berkeley professor who directs the school's Center for Catastrophic Risk Management, said the flaw led to natural gas shooting up a riser pipe from the wellhead to the rig above, where it exploded. Eleven workers are missing and presumed dead from the accident, which has led to a leak of 210,000 gallons of oil a day.

Bea said that the cement was tainted with the same slushy gas hydrate that scuttled BP's plan to contain the oil with a giant box last week.

The hydrates hidden in the cement turned to gas and seeped into the well column, Bea says.

Not all experts agree that the evidence suggests this. But most agree with Bea's general point: Cement used to close up the well was leaky.

The issue was a focal point of congressional hearings Tuesday on the cause of the accident. "The one thing we do know is that on the evening of April 20th there was a sudden, catastrophic failure of the cement, the casing, or both," Steven Newman, chief executive of Transocean, the rig's owner, told the Senate Environment and Public Works Committee.

A Halliburton official testifying at the same hearing defended the company's cementing. The casing "was cemented some 20 hours prior to the tragic incident, and had the [blowout preventer] functioned as expected, this catastrophe may well not have occurred," said Halliburton executive Tim Probert.

Bea and other experts say a sound-wave test can detect openings or weak spots in cement. Bea said eight transcripts he has reviewed suggest this test was not run. BP declined to comment until the investigation was complete. Halliburton officials did not respond by Tuesday night to a reporter's question about whether the test had been run.

Cement is used in many stages of drilling, including sealing oil wells once exploration is complete. It is supposed to form an impermeable seal to keep out pressurized natural gas. The Deepwater Horizon had just finished this process when the blowout happened.

Cement can fail for many reasons, including contamination from drilling mud or other substances. Bea said he believes that in this case, hydrates — exotic compounds that only exist in high-pressure conditions — mixed with the cement while it was still mushy.

When workers eased pressure in the well by replacing drilling mud with seawater, those hidden hydrate pockets turned from solid to gas and shot toward the surface, Bea said. "They didn't realize it had mixed with the cement," he said.

David Valentine, a geochemist at UC Santa Barbara, said that Bea's theory is possible — provided the cement was cool enough.

Regardless of the exact cause of the cement flaw, a series of other failures were needed to produce the blowout, experts say, including the possible failure of synthetic seals and a blowout preventer.

jill.leovy@latimes.com

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