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Gulf oil spill: The story so far

The effort to contain the Gulf oil spill has had more twists and turns than a mystery novel. This rundown of events so far also shows what is ahead in the struggle to clean up the Gulf of Mexico.

By Staff writer / June 29, 2010

Aboard Development Driller 11 in the Gulf, workers install casing for one of two wells being drilled to intercept and then plug the blown-out well.

Peter Andrew Bosch/AP

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Since the Deepwater Horizon rig explosion April 20, BP and the federal government have struggled to control the oil spill that has followed. The complex effort has involved several attempts to stem the flow of oil at the wellhead, amid uncertainty about how much oil, exactly, has been flowing into the Gulf of Mexico. Now in its third month, the Gulf oil spill seems likely to continue at least until August. Here is an accounting of some of the most important – and confusing – developments.

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What's been done to stop the oil flow?

May 29 was a turning point in BP's efforts at the bottom of the Gulf. That was the day the so-called "top kill" effort – BP's only bid to stop, rather than contain, the flow of oil – failed. The result: The company essentially admitted defeat in its bid to turn off the spigot before August.

Now, the only way BP believes it can shut down the well permanently is to drill a relief well that intersects the leaking well. Then, BP plans to pump heavy drilling mud through the relief well into the leaking well to slow the flow of oil. It could then cement the leaking well near the source.

The primary relief well and a backup are scheduled to be finished at some point in August. The task of intersecting a well with a relief well, however, is difficult and could require several attempts, pushing back the actual shutdown date.

Until then, BP is trying to limit the damage by collecting oil at the source.

After two failed attempts to collect oil via a containment dome and then a siphon, BP tallied its first success with a containment cap in early June. In short, BP cut the riser pipe that once led from the blowout preventer to the surface – it had fallen to the seafloor like a crumpled garden hose – and replaced it with a cap.

The cap has been doing its job reasonably well, although a June 23 mishap meant that it had to be removed for a day. When it is working, it has captured about 15,000 barrels of oil a day (630,000 gallons), which have been processed on the surface by a ship called the Discoverer Enterprise.

On June 16, a second ship, the Q4000, linked to a valve on the side of the blowout preventer and began burning off about 10,000 barrels a day. A third ship with the capacity to burn 25,000 barrels of oil a day, the Helix Producer, was set to hook up to another valve on the blowout preventer by June 29. High seas forced a delay in that plan. Coast Guard Adm. Thad Allen, who is leading the federal response to the spill, said that the ship will proceed with its mission as soon as conditions permit.

The Helix Producer is expected to be involved in oil collection for the foreseeable future. The Q4000 is scheduled to be replaced by a ship with larger capacity – 25,000 barrels a day – in mid-July.

Still, the containment cap is essentially a stopgap measure. BP would like to replace it with a more robust cap, called the overshot tool.

The overshot tool promises several advantages: It could capture more oil, in part because it would be bolted directly to the blowout preventer, potentially providing a better seal. Also, it would have two, more-flexible risers that ships could connect to and disconnect from more easily in the event of a hurricane.

The danger is that the existing cap would need to be removed, allowing oil to flow freely until the new one is affixed. Moreover, the current system is the only one that has worked.

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