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Gulf oil spill: the 51 minutes that led to disaster

Fifty-one minutes before the explosion and fire aboard Deepwater Horizon, workers on the rig sensed something was wrong. Within an hour, oil was gushing from the mangled wellhead. Here’s what we know so far.

By Staff writer / May 26, 2010

A fire aboard the mobile offshore drilling unit Deepwater Horizon in the Gulf of Mexico 52 miles southeast of Venice, La. The rig exploded at about 10 p.m. on April 20. Despite firefighting efforts, the rig sank on April 22. The resulting oil spill could be the worst in US history.

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Fifty-one minutes before it exploded, the oil well beneath the Deepwater Horizon drilling rig began showing signs of impending doom.

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The date was April 20, the time early evening. Rig workers were pumping fluid into the well, getting ready to cap it and move on to another job. But more fluid was coming out than was going in. What was going on?

Forty-one minutes before the explosion they shut down the pump for a “sheen test” – an EPA-mandated step intended to spot free oil floating to the surface. With no pump running, the well flow should have stopped. It didn’t. Fluid kept coming up – and sensors showed that pressure in the drill pipe unexpectedly was increasing.

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Eighteen minutes before the explosion the situation began to escalate. Pressures began to reach abnormal levels. Mud was coming to the surface. The pump – which had been restarted – was abruptly shut down.

We don’t really know what happened in the next fateful minutes. There’s evidence the crew tried some sort of “mechanical intervention,” according to a congressional memo. But the flow of fluid and the increase in pressure continued to spike.

Oil gushed from the mangled wellhead

At about 10 p.m, the well exploded. One hundred and twenty six people were on board the Deepwater Horizon rig at the time. Eleven were killed and 15 injured. Oil began gushing from the mangled wellhead at a tremendous rate, and a slower, ecological disaster began to occur – an oil spill that may yet have a profound effect on the energy future of the US.

Investigations into the Deepwater Horizon’s last hours undoubtedly will stretch on for months, if not years. At the moment, everyone is blaming someone else. BP, for instance, which owns the lease on the well, is pointing at the Deepwater Horizon rig’s owner, Transocean, and the contractor hired to cement the well, Halliburton, as main culprits.

But documents pulled together by the House Energy and Commerce Committee Subcommittee on Oversight provide some idea of Deepwater’s final days. Combined with other sources, they provide our best look so far at what happened – if not why.

One clue may be an alleged decision by BP to replace heavy drilling fluid in the well with lighter seawater, in an effort to cut costs and move as fast as possible to production.

The seawater was supposed to hold down the petroleum surging up from beneath the sea while workers capped the well with cement to seal it. It didn’t work.

'BP was taking shortcuts'

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