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Static kill successfully halts Macondo spill

BP stopped the flow of oil from the Macondo well in the Gulf of Mexico with its static-kill procedure on 3 August, by pumping heavy mud through the blowout preventer (BOP) and into the well

After eight hours of pumping, the process ended and BP said that well pressure was "being controlled by the hydrostatic pressure of the drilling mud – the desired outcome of the static kill".

Two relief wells – the first of which is expected to intercept the Macondo well over the coming weeks – remain the ultimate solution. These will break into the well from different angles, at 14,000 feet and 17,000 feet below the sea bed, pumping mud and cement into the well to seal it off in a procedure known as bottom kill.

The flow of oil has been stemmed since 15 July, when BP fitted a cap onto the BOP. Although a temporary solution, this stopped the leak for the first time since 20 April, bringing three months of attempted interventions to an end (see below).

But BP's problems are not over. Under the US Clean Water Act, the company faces charges of $1,100 for each barrel of oil spilled. The penalty will rise to $4,300 a barrel if the company is found to have been guilty of gross negligence. This means BP stands to be fined between $5.4bn and $21bn, based on the latest estimates from US government scientists that 4.9m barrels of oil poured into the US Gulf following the Deepwater Horizon explosion.

Spill containment timeline

25 April – efforts to trap and burn oil on the sea surface while trying to activate the BOP fail.

2 May – work begins on the first of two relief wells, due to reach their target in mid-August.

7 May – a 98-tonne cofferdam (containment dome) is lowered onto the main leak, to divert the oil to the surface for collection. This fails because of the formation of methane hydrate crystals that block the spout.

16 May – as oil starts to reach the shore, BP fits a four-inch tube into the drilling pipe and captures 1,000 b/d and then 5,000 b/d of oil.

26 May – the top-kill process is attempted, which involves forcing heavy mud and debris – including golf balls and shredded tyres – into the well. The procedure fails on 30 May.

4 June – a containment cap is fitted to the well, with reasonable success, allowing the capture of around 25,000 b/d.

15 July – BP says it has stopped the leak after replacing the containment cap with a tighter-fitting capping stack.

3 August – a static-kill procedure holds the pressure after eight hours of pumping heavy mud and concrete into the well.

5 August – BP is given the go-ahead from the national incident commander, Thad Allen, to start pumping cement into the well as the second stage of the static-kill procedure.

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