Chemical Guide

BP to begin tests to close valves on new containment cap in Gulf of Mexico and hopes to temporarily stop oil gushing from wellhead

BP has fitted a larger, tighter-fitting containment cap on the ruptured Gulf of Mexico wellhead that has been gushing with oil since the Deepwater Horizon explosion on 20 April.Crude oil continues to spill into the sea, but the company wants to begin testing the new cap’s internal pressure this morning by closing its valves and hopes to be able to stop the flow until more permanent measures can be taken.

BP warned that success was not certain: “It is expected, although cannot be assured, that no oil will be released to the ocean for the duration of the test. This will not, however, be an indication that flow from the wellbore has been permanently stopped.”

BP said it does not expect to plug the undersea geyser for good before mid-August, after intercepting the rupture point with one of two relief wells now being drilled.

Former US coastguard Admiral Thad Allen, who is overseeing the US government’s spill response, said that if the cap works it will be used to resume the siphoning of oil to ships on the surface until the ruptured well can be permanently plugged.

The new cap-and-seal stack, which is larger than the one removed on Friday and bolted over the top of the wellhead rather than clamped loosely over it, is designed to capture three times more leaking oil, or virtually the entire flow.

Allen said it was possible the new cap could be used to shut down the wellhead again temporarily “for a period of time, such as during a hurricane or bad weather”.

Doug Suttles, BP’s chief operating officer of exploration and production, suggested the cap might be used to keep the well closed for a longer stretch. “Depending on the results, we’ll either continue to contain the flow while we wait on the relief well or potentially be able to close the flow in,” he said.

For the duration of the well-integrity tests, two other subsea oil-siphoning systems, one of them just brought online on Monday, will be turned off, BP said.

Suttles said that even if the cap can shut off the flow, which is one mile (1,600m), below the surface, BP must still finish the relief well at an even greater depth so it can pump heavy drilling fluid and then cement to permanently plug the leak.

On Monday, the first of two relief wells, begun on 2 May, was about 190ft (58m) from intersecting the blown-out well that is 13,000ft beneath the seabed, Suttles said. The relief well could reach its target by the end of July, BP says, keeping it on schedule to actually kill the leak by mid-August.

If the relief wells fail, BP could install a new permanent oil-capture system by late August or early September, Kent Wells, senior vice president of exploration and production, told President Barack Obama’s commission investigating the spill.

Source: guardian.co.uk