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BP's Macondo well capped at last

Oil has stopped flowing out of control from BP's blown-out Macondo well in the deep water Gulf of Mexico

At 2:25 pm US Central Time, on 15 July, remotely operated vehicles (ROVs) closed the last of three valves on the newly installed containment cap, an 80 tonne, 40 foot-tall series of valves and pressure-monitoring gauges, fitted atop the well, in about 5,000 feet of water.

Engineers in shipboard control rooms and at BP's headquarters in Houston began monitoring pressure levels inside the cap for signs that the structural integrity of the well, which extends about 13,000 feet underground, is sound. Pressures that failed to climb above 6,000 pounds per square inch (psi) would indicate that oil could be leaking through cracks in the well bore or casing. Response crews hoped for at least 7,500 psi, the figure initially thought to signify that the sealed well would be strong enough to contain the oil. The pressure built slowly, finally settling at around 6,800 psi. ROVs scrutinising the ocean floor around the well bore and taking sonar readings saw no signs of possible leaks.

In a technical briefing on 18 July, BP chief operating officer Doug Suttles argued that the lower-than-expected reading was consistent with models demonstrating that the well's pressure had been depleted as the oil flowed freely for three months. However, Retired US Coast Guard admiral Thad Allen, leader of the federal oil-spill response, expressed concerns about the condition of the well. He extended the integrity tests, which initially were scheduled to take 48 hours, and ordered more extensive monitoring for leaks.

Allen and BP officials have presented differing views of what would happen after the test concludes. On 15 July, Allen said: "It remains likely that we will return to the containment process using this new stacking cap connected to the risers to attempt to collect up to 80,000 barrels a day of oil until the relief well is completed."

In the technical briefing three days later, Suttle said he hoped the integrity tests would continue until the well is killed. "No one wants to see oil flowing back into the sea and to re-initiate containment would require that to occur," he said.

The decision rests with Allen. Either way, capping the Macondo well is only a temporary measure until one of two relief wells being drilled kills it permanently by pumping down cement and heavy drilling mud. "The earliest we would intercept the original well bore and start the kill operation still looks like the last few days of July," Suttle explained, "and that operation, depending how it progresses, could take us into the middle of August." Work on the second relief well, already drilled to a depth of 18,874 feet, has been halted until the results of the first well have been assessed.

The success of the cap in halting the hydrocarbon stream came after a string of failures that included containing the oil with a 100 tonne dome placed over the wellhead, lowering a 2 tonne top hat over the spill and an attempt to top-kill the well by pumping in drilling mud and other debris. Capping the well marked a significant milestone in the chronology of events that have unfolded since the blowout occurred on 20 April, killing 11 people, sending the Deepwater Horizon drilling rig to the ocean floor and causing the largest oil spill in US history.

"There's a lot to do even once we get this well completely sealed off where it can never flow again," Suttle said. "We have to complete the clean-up and mitigate the impacts to both the environment and the people in the region."

Meanwhile, as US Congressional hearings into the cause and implications of the blowout continue, BP is now figuring prominently in another matter under scrutiny on Capitol Hill.

The issue involves Abdelbaset Ali Mohmed al Megrahi, who was released from prison in August 2009 after spending eight years of a life sentence for the 1988 bombing of Pan Am Flight 103 over Lockerbie, Scotland, which killed 270 people. Scottish justice secretary Kenny MacAskill made the decision to free al Megrahi, in August 2009, after the Libyan citizen was diagnosed with terminal prostate cancer and given only three months to live. He remains alive today.

BP acknowledged it had expressed concerns to the UK government at the time that delays in concluding a prisoner-transfer agreement with Libya could have negative consequences for UK commercial interests in the country. But Scottish officials say MacAskill had rejected Megrahi's release under a prisoner-transfer agreement and had not been in contact with BP about his release. Libyan officials ,and UK prime minister David Cameron have also denied that al Megrahi's release was arranged in exchange for ratification of a BP exploration agreement. The Senate foreign relations committee was due to hold a hearing on the case in July.

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