Tuesday, August 3, 2010

Methods That Have Been Tried to Stop the Leaking Oil : The New York Times



Methods That Have Been Tried to Stop the Leaking Oil

Efforts to Suppress the Flow of Oil

Since a fire engulfed the Deepwater horizon rig in the Gulf of Mexico on April 20, engineers have attempted a number of techniques to slow or stop the torrent of oil leaking from the wellhead 5,000 feet below the surface.


BP is expected to begin the process of sealing the Macondo well with the “static kill” as early as Monday. The method is similar to the top kill that failed in early June and would use existing equipment and plumbing. But this time, engineers can pump mud slower and at lower pressure because a new cap atop the well had stemmed the flow of oil. After the static kill, BP will proceed with killing the well from the bottom with the relief well.
Source: BP


With the new sealing cap in place, engineers will test the well’s pressure to determine its integrity.
Source: BP


In a procedure that would take several days, BP removed the well cap that was put in place on June 3 to replace it with a new one with the potential to completely stop the flow from the well. The new cap has some of the same types of components as the blowout preventer. Once installed, engineers will take pressure readings for up to two days. If the pressure is at an anticipated level, the cap could remain closed, ending the gusher.
Source: BP


By mid-July, BP expects to have a total of four vessels on site to collect and process oil and gas. The Q4000 will be replaced by another vessel, Toisa Pisces, which will be connected to one of two floating risers that can be disconnected in the event of a hurricane.
Source: BP


A second containment system has begun siphoning oil and gas from the leaking well. BP estimates the system will carry 5,000 to 10,000 barrels a day to the surface, supplementing the roughly 15,000 barrels collected daily by a containment cap on top of the blowout preventer.
Using equipment originally put in place to inject heavy drilling mud during the failed “top kill” procedure last month, the new system extracts oil and gas directly from the blowout preventer, passes it through a manifold on the seafloor and pipes it up to the Q4000 surface vessel.
The Q4000 has no storage capacity and will burn the oil and gas.
Source: BP


A cap placed over the upper portion of the leaking well was funneling some oil and gas to a surface ship, though oil continued to billow from under the lip and through four open vents on top of the device. Methanol is being pumped into the cap to prevent the formation of icy hydrates that could block the mile-long pipe rising from the cap. Engineers hope to capture more oil by progressively closing the cap vents.
Source: BP


After the failure of the top kill operation, BP began a new operation to cap the well. The damaged pipe will be cut from the blowout preventer, and a dome will be lowered over it to catch the spewing oil.
The new riser pipe will have a 6.625 inch internal pipe to capture leaking oil and gas. Methanol and warm seawater will be pumped down the riser to insulate the smaller pipe and prevent the formation of ice crystals which caused the earlier containment dome to fail.
Source: BP


BP tried two more operations, called the “junk shot” and the “top kill,” to stop the gushing oil. In the “top kill,” heavy drilling liquid is pumped into the well until the weight of the liquid overcomes the pressure of the rising oil. The “junk shot” involves injecting objects like golf balls to clog the blowout preventer, the stack of valves at the top of the well.
Source: BP technical briefings


After several unsuccessful attempts, BP inserted a mile-long tube into the broken riser pipe to divert some of the oil to a drill ship on the surface some 5,000 feet above the wellhead. The tube siphoned off about 22,000 barrels of oil over nine days, but was shut off once the “top kill” operation began.


BP constructed a four-story containment dome, intended to control the largest of the leaks. As the dome was lowered, crews discovered that the opening was becoming clogged by an icy mix of gas and water. The dome was set down on the seabed, 650 feet away from the leak, as officials decided how to proceed.
Source: BP


BP is drilling relief wells that may be used to plug its runaway well in the Gulf of Mexico. Once one of the new wells intersects the existing well, heavy drilling mud, followed by cement, will be used to stop the oil from leaking.
Source: BP


BP officials began injecting chemical dispersants underwater, near the source of the leaks. The dispersants, usually used on the water surface, is intended to break up the oil before it rises. The full environmental impact of the technique is unknown, but the E.P.A. has directed BP to change to a less toxic chemical than it had originally chosen.
Source: BP


The quickest way to stop the leak would have been to activate the well’s blowout preventer, a valve designed to seal off the well in an emergency. But several efforts to activate the blowout preventer failed.
Sources: United States Coast Guard; BP

How the Leak Started

Gerald Herbert/Associated Press
On April 20, the Deepwater Horizon, a drilling rig 50 miles off the coast of Louisiana in the Gulf of Mexico, exploded into flames. Two days later the rig sank, causing the 5,000 foot pipe that connected the wellhead to the drilling platform to bend. On April 24, robotic devices discovered two leaks in the bent pipe, nearly a mile below the ocean surface.

Gulf Spill Is the Largest of Its Kind, Scientists Say: The New York Times

【出展リンク】: http://www.nytimes.com/2010/08/03/us/03spill.html?ref=global-home

Gulf Spill Is the Largest of Its Kind, Scientists Say

NEW ORLEANS — The BP spill is by far the world’s largest accidental release of oil into marine waters, according to the most precise estimates yet of the well’s flow rate, announced by federal scientists on Monday.
Nearly five million barrels of oil have gushed from BP’s well since the Deepwater Horizon rig exploded on April 20, according to the latest data. That amount outstrips the estimated 3.3 million barrels spilled into the Bay of Campeche by the Mexican rig Ixtoc I in 1979, previously believed to be the world’s largest accidental release.
The BP spill was already thought to be the largest spill in American waters, but it was unclear whether it had eclipsed Ixtoc.
“We’ve never had a spill of this magnitude in the deep ocean,” said Ian R. MacDonald, a professor of oceanography at Florida State University.
“These things reverberate through the ecosystem,” he said. “It is an ecological echo chamber, and I think we’ll be hearing the echoes of this, ecologically, for the rest of my life.”
Federal science and engineering teams, citing data that are “the most accurate to date,” estimated that 53,000 barrels of oil a day were pouring from the well just before BP was able to cap it on July 15. They also estimated that the daily flow rate had diminished over time, starting at about 62,000 barrels a day and decreasing as the reservoir of hydrocarbons feeding the gusher was gradually depleted. Before Monday’s announcement, federal scientific teams had estimated the spill in a range from 35,000 to 60,000 barrels a day.
The teams believe that the current estimates are accurate to within 10 percent. They also reported that of the roughly 4.9 million barrels that had been released from the well, about 800,000 had been captured by BP’s containment efforts. That leaves over four million barrels that gushed into the Gulf of Mexico from April 20 to July 15.
As the estimates of the number of barrels spilled increases, so, too, do the penalties under the Clean Water Act, which calls for fines of $1,100 per barrel, or $4,300 per barrel if the government finds that gross negligence led to the spill.
At 4.9 million barrels, that means that the total fine could be $5.4 billion — and, if gross negligence led to the spill, $21 billion. If BP successfully argues that the 800,000 barrels it has recovered should mitigate the penalty, then the figure drops to $4.5 billion and $17.6 billion, respectively.
The amount of oil estimated to be pouring from the well has been a matter of dispute from the earliest days of the spill. Federal and BP officials initially announced that no oil appeared to be leaking, then 1,000 barrels a day, then 5,000 a day, frequently repeating that spill estimates are rough at best and that the main goal was to stop the well. But criticism mounted that no effort was being made to measure the leak with more certainty.
The Obama administration announced the creation of a scientific group dedicated to analyzing the flow rate, which came up with a new estimate of 12,000 to 19,000 barrels a day in late May, a figure that was met with skepticism. That, too, was later revised upward several times before Monday’s announcement. Previous estimates came from analysis of videos from remote-controlled vehicles at the wellhead, modeling of the reservoir and measurements of the oil that was collected by surface ships in the response effort.
After BP capped the well, these measurements could be reinforced by pressure readings within the well. Those pressure readings were compared with pressure estimates when the well was first drilled to determine whether the rate had changed over time, which it apparently had.
The government is continuing to study the data and may refine the estimate.
Meanwhile, BP continued efforts Monday to permanently seal the well. It said it was preparing to conduct final testing on Tuesday to determine whether to go ahead with a plan to pump heavy drilling mud into the runaway Macondo well, in hopes of permanently sealing it by the end of the week.
During the tests, a surface ship will slowly inject small amounts of mud into the well to make sure the mud will reach the oil reservoir from the column of pipes and valves that sit atop it. If that is accomplished, BP will pump higher volumes of mud, and possibly cement, into the well, in an operation known as a static kill or bullheading.
BP executives said Monday that they expected positive results from the tests, which will also check the pressure of the well to ensure that it is safe to pump the mud.
The efforts come 18 days after BP placed a tight-fitting cap on the well that put a temporary end to months of leaking. Engineers had planned to begin the tests on Monday but had to delay when they found a small hydraulic leak in the capping control system above the well.
Kent Wells, senior vice president for exploration and production at BP, said on Monday that a day or two after the pumping of mud began, engineers would consider pumping cement into the well, which could permanently plug it. Engineers might also decide to wait for a relief well to be completed before pumping cement in. There is also a chance that they will pump cement during the static kill and later through the relief well, to make sure the runaway well is sealed.
“We want to end up with cement in the bottom of the hole, completely filling the entire Macondo well,” Mr. Wells said Monday. “Whether that comes from the top or whether it comes from the relief well, those will be decisions made along the way.”
An estimated 2,000 pounds of mud is to be flooded into the well this week.
Thad W. Allen, the retired Coast Guard admiral who is leading the federal response to the spill, cautioned against rushing to declare the static kill a final victory over the well. “I don’t think we can see this as the end-all, be-all, until we actually get the relief wells done,” he said.
Mr. Wells said the last 100 feet of the first of two relief wells should be completed by Aug. 15. A final killing of the well by pouring mud and cement just above the reservoir could take a few days or as much as a few weeks. If the first relief well somehow misses its target, a second one is being drilled for insurance.

Campbell Robertson reported from New Orleans, and Clifford Krauss from Houston. Catrin Einhorn and John Schwartz contributed reporting from New York.


【出展リンク】: http://www.amakiblog.com/archives/2010/07/30/#001649



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