ON THE GULF OF MEXICO (AP) - The deadly blowout of an oil rig in
the Gulf of Mexico was triggered by a bubble of methane gas that
escaped from the well and shot up the drill column, expanding
quickly as it burst through several seals and barriers before
exploding, according to interviews with rig workers conducted
during BP's internal investigation.
While the cause of the explosion is still under investigation,
the sequence of events described in the interviews provides the
most detailed account of the April 20 blast that killed 11 workers
and touched off the underwater gusher that has poured more than 3
million gallons of crude into the Gulf.
Portions of the interviews, two written and one taped, were
described in detail to an Associated Press reporter by Robert Bea,
a University of California Berkeley engineering professor who
serves on a National Academy of Engineering panel on oil pipeline
safety and worked for BP PLC as a risk assessment consultant during
the 1990s. He received them from industry friends seeking his
expert opinion.
A group of BP executives were on board the Deepwater Horizon rig
celebrating the project's safety record, according to the
transcripts. Meanwhile, far below, the rig was being converted from
an exploration well to a production well.
Based on the interviews, Bea believes that the workers set and
then tested a cement seal at the bottom of the well. Then they
reduced the pressure in the drill column and attempted to set a
second seal below the sea floor. A chemical reaction caused by the
setting cement created heat and a gas bubble which destroyed the
seal.
Deep beneath the seafloor, methane is in a slushy, crystalline
form. Deep sea oil drillers often encounter pockets of methane
crystals as they dig into the earth.
As the bubble rose up the drill column from the high-pressure
environs of the deep to the less pressurized shallows, it
intensified and grew, breaking through various safety barriers, Bea
said.
"A small bubble becomes a really big bubble," Bea said. "So
the expanding bubble becomes like a cannon shooting the gas into
your face."
Up on the rig, the first thing workers noticed was the sea water
in the drill column suddenly shooting back at them, rocketing 240
feet in the air, he said. Then, gas surfaced. Then oil.
"What we had learned when I worked as a drill rig laborer was
swoosh, boom, run," Bea said. "The swoosh is the gas, boom is the
explosion and run is what you better be doing."
The gas flooded into an adjoining room with exposed ignition
sources, he said.
"That's where the first explosion happened," said Bea, who
worked for Shell Oil in the 1960s during the last big northern Gulf
of Mexico oil well blowout. "The mud room was next to the quarters
where the party was. Then there was a series of explosions that
subsequently ignited the oil that was coming from below."
According to one interview transcript, a gas cloud covered the
rig, causing giant engines on the drill floor to run too fast and
explode. The engines blew off the rig and set "everything on
fire," the account said. Another explosion below blew more
equipment overboard.
BP spokesman John Curry would not comment Friday night on
whether methane gas or the series of events described in the
internal documents caused the accident.
"Clearly, what happened on the Deepwater Horizon was a tragic
accident," said Curry, who is based at an oil spill command center
in Robert, La. "We anticipate all the facts will come out in a
full investigation."
The BP executives were injured but survived, according to one
account. Nine rig crew on the rig floor and two engineers died.
"The furniture and walls trapped some and broke some bones but
they managed to get in the life boats with assistance from
others," said the transcript.
The reports made Bea, the 73-year-old industry veteran, cry.
"It sure as hell is painful," he said. "Tears of frustration
and anger."
On Friday, a BP-chartered vessel lowered a 100-ton
concrete-and-steel vault onto the ruptured well, an important step
in a delicate and unprecedented attempt to stop most of the gushing
crude fouling the sea.
"We are essentially taking a four-story building and lowering
it 5,000 feet and setting it on the head of a pin," BP spokesman
Bill Salvin told The Associated Press.
Underwater robots guided the 40-foot-tall box into place in a
slow-moving drama. Now that the contraption is on the seafloor,
workers will need at least 12 hours to let it settle and make sure
it's stable before the robots can hook up a pipe and hose that will
funnel the oil up to a tanker.
"It appears to be going exactly as we hoped," Salvin said on
Friday afternoon, shortly after the four-story device hit the
seafloor. "Still lots of challenges ahead, but this is very good
progress."
By Sunday, the box the size of a house could be capturing up to
85 percent of the oil.
The task became increasingly urgent as toxic oil crept deeper
into the bays and marshes of the Mississippi Delta.
A sheen of oil began arriving on land last week, and crews have
been laying booms, spraying chemical dispersants and setting fire
to the slick to try to keep it from coming ashore. But now the
thicker, stickier goo - arrayed in vivid, brick-colored ribbons -
is drawing ever closer to Louisiana's coastal communities.
There are still untold risks and unknowns with the containment
box: The approach has never been tried at such depths, where the
water pressure is enough to crush a submarine, and any wrong move
could damage the leaking pipe and make the problem worse. The
seafloor is pitch black and the water murky, though lights on the
robots illuminate the area where they are working.
If the box works, another one will be dropped onto a second,
smaller leak at the bottom of the Gulf.
At the same time, crews are drilling sideways into the well in
hopes of plugging it up with mud and concrete, and they are working
on other ways to cap it.
Investigators looking into the cause of the explosion have been
focusing on the so-called blowout preventer. Federal regulators
told The Associated Press Friday that they are going to examine
whether these last-resort cutoff valves on offshore oil wells are
reliable.
Blowouts are infrequent, because well holes are blocked by
piping and pumped-in materials like synthetic mud, cement and even
sea water. The pipes are plugged with cement, so fluid and gas
can't typically push up inside the pipes.
Instead, a typical blowout surges up a channel around the
piping. The narrow space between the well walls and the piping is
usually filled with cement, so there is no pathway for a blowout.
But if the cement or broken piping leaves enough space, a surge can
rise to the surface.
There, at the wellhead of exploratory wells, sits the massive
steel contraption known as a blowout preventer. It can snuff a
blowout by squeezing rubber seals tightly around the pipes with up
to 1 million pounds of force. If the seals fail, the blowout
preventer deploys a last line of defense: a set of rams that can
slice right through the pipes and cap the blowout.
Deepwater Horizon was also equipped with an automated backup
system called a Deadman. It should have activated the blowout
preventer even if workers could not.
Based on the interviews with rig workers, none of those
safeguards worked.


Permalink | Comments