BP ready for final phase of Gulf oil leak repair

BP yesterday began pumping mud into its blown-out Gulf well, under the "static kill" procedure that is the penultimate step before putting a final end to what is now believed to be the worst accidental oil spill in history.

BP crews began the long-awaited effort yesterday afternoon, hours after engineers had dealt with yet another 11th-hour hitch - this time a leak in the valve on the well's temporary cap installed on 15 July.

Thad Allen, the US official in charge of relief operations, confirmed the start of "static kill" tests. The mud will initially be injected at a very low rate, he said, because "we don't know the exact condition of the well".

If all goes to plan, the "static kill" should be completed in two days. BP engineers now say this operation alone might now be enough to do the job, meaning that the two relief wells which have almost reached the damaged one might in fact no longer be needed.

But the company is taking no chances, after a disaster that has been a calamity for the Gulf of Mexico, for local residents and BP's reputation and finances, not to mention the 11 workers who lost their lives in the initial explosion on the Deepwater Horizon rig on 20 April.

Even if the "static kill" is a success, the first relief well will nonetheless be completed, said Kent Wells, a BP executive. "Even if we were to pump the cement from the top, we will still continue with the relief well to confirm that the well is dead," he said. Either way, "we want to end up with cement in the bottom of the hole".

Over the last fortnight, since the experimental cap first staunched the leak and the surface oil all but disappeared, there have been suggestions that the damage might not be as bad as once feared. But a new government-sponsored analysis may dash such optimism.

The study, supervised by the US Department of Energy, concluded that the spill had spewed 4.9 million barrels, or 205 million gallons, of oil into the Gulf over the three months, first at a rate of 62,000 barrels a day before tapering to 53,000 bpd as pressure in the ruptured well eased. The 62,000 bpd figure is more than 12 times government and company estimates in the first weeks after the disaster.

If so, then the Macondo well spill is half as large again as the Ixtoc 1 blowout in the Gulf in 1979, the worst such accident to date, and equivalent to an Exxon Valdez-size spill every four or five days.

In all some 1.2 million barrels, a quarter of the total spill, have been accounted for. BP's surface operations captured 800,000 barrels, while 400,000 more are reckoned to have been burned, skimmed off the surface, or broken up by dispersants. But the fate of the rest is a mystery. Some may have been eaten by microbes, the rest may be in huge plumes below the Gulf's surface. However scientists warn that even if the well is definitively sealed this week, the after-effects of the spill will be felt for years, perhaps decades.