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Photo: Underwater video still of the BP oil cap being sealed

Part of the containment capping stack at the BP Macondo well is seen in a September 4 video grab.

Photograph by BP/Reuters

Eric Skalac

For National Geographic News

Published April 20, 2011

This story is part of a special series that explores energy issues. For more, visit The Great Energy Challenge.

It was the most closely watched oil well kill in history.

On grainy, monochrome subsea video, the world was able to keep track of the BP gusher and all the failed efforts to bring it under control, a process that took 87 days. Then, a heavy array of valves and pipes—a temporary cap—was lowered into place. After that, the static kill, and still later, the bottom kill: Cement was poured and pumped into the hole to create a final, permanent seal.

How permanent is that plug, given the volatile conditions in the Gulf of Mexico, and the fierce behavior of this high-pressure well that was the source of the worst offshore oil spill in U.S. history?

(Related: Gulf Oil Spill: One Year Later)

As it turns out, the stability of the BP well seal is one of the few things on which the giant oil company and its critics agree. David Pettit, an attorney and blogger for the Natural Resources Defense Council, says he believes that the Macondo well will stay secure in part because of “all the attention that was paid to it.”

The U.S. government admitted last year that there are plenty of former oil wells in the Gulf of Mexico that are not as closely scrutinized. A few days before the BP well was officially declared dead in September, the Obama administration ordered the oil industry to take steps to seal 3,500 wells secured only with temporary subsurface safety valves, and to dismantle 650 production platforms that were no longer being used. An investigation by the Associated Press last summer, while all eyes were riveted on the BP gusher, drew attention to the problem of abandoned wells that were not being watched on the same seafloor.

Small Companies, Big Expense

Properly closing a well—by plugging it with cement and removing any remaining surface structures—can be expensive, said Robert Bea, a professor of ocean engineering at the University of California, Berkeley. “As you might guess, some operators want to defer these activities as long as they can to save money,” he said. By some reports, experts calculated the cost of industry compliance with the Obama order could approach $3.5 billion.

(Related: Satellite Photos of the Gulf Oil Spill's Evolution)

That’s a potentially large bill racked up by what could be a lot of small companies. William Abel, a petroleum engineer whose Houston-based well-drilling and control company helped cap sabotaged wells in the first Persian Gulf war, said there are numerous “mom-and-pop” operations that own a handful of wells. “They get all the production out of them, and then they just disappear and leave the well sitting there,” he said.

Abandoned platforms on the water’s surface are of the greatest concern, Bea and Abel said, because they can be damaged in severe weather like the hurricanes that sometimes tear through the Gulf of Mexico in the late summer and fall. A damaged surface platform in turn can cause the well beneath to leak.

Secure Beneath the Sea

But a mile beneath the water’s surface, plugged with cement from both top and bottom, the seal of BP’s Macondo well would not be affected by storms whipping above in the Gulf of Mexico.

After the tight-fitting temporary cap stopped the flow of oil from Macondo last July, BP embarked on a two-part plan to permanently seal the well. The first step was a “static” kill, in which heavy mud and cement were pumped through the blowout preventer and into the well. It was similar to a “top” kill attempt that failed earlier; the tremendous pressure that had to be overcome while the well was still flowing rendered that effort futile. That failure signaled that BP and government authorities had dramatically underestimated the flow rate from Macondo, which ultimately spilled 4.9 million barrels (205.8 million gallons/779 million liters) into the Gulf.

(Related: "While BP Eyes Return to the Gulf, Safeguards Debated")

A better understanding of the furious pressure in the well guided engineers to design and deploy the temporary cap by mid-July. After that, the static kill worked, allowing BP to fill the entire well with cement from the sea floor down to the reservoir, 18,000 feet (5,486 meters) below sea level. The job was finished off when a second well—a relief well that BP had begun drilling soon after the catastrophic April 20 blowout—finally intercepted the Macondo well on September 16. Cement was pumped into Macondo from the relief well for the final bottom kill.

And the Macondo well, which had tapped into a reservoir estimated to hold 50 million barrels of oil, will not be leaking any more of it into the Gulf, the experts say. “If it was going to leak, it would be leaking now—the early time is the critical time,” says Darryl Bourgoyne, director of the Petroleum Engineering Research & Technology Transfer Laboratory at Louisiana State University.

Eric Skalac is a reporter for Medill News Service in Washington, D.C.

Editor's note: A previous version of this story incorrectly called the Deepwater Horizon oil spill the worst in U.S. history. At 5 million barrels, it was the worst U.S. offshore spill, but on land it was surpassed by the Lakeview gusher in 1910 and 1911, which spilled 9.4 million barrels of oil in California's San Joaquin valley.

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