Image: Vessels work at the site of the Deepwater Horizon incident
Win McNamee  /  Getty Images
Vessels work at the site of the Deepwater Horizon incident as seen from inside a Coast Guard flight over the site August 10 off the shore of Louisiana.
msnbc.com staff and news service reports
updated 8/13/2010 4:51:30 PM ET 2010-08-13T20:51:30

Ending days of uncertainty, the incident chief for the busted BP well said Friday that BP experts and government scientists agree a relief well needs to be finished to completely kill the busted well, but just how to do so is still being discussed.

"Everybody's in agreement we need to move ahead with the relief well; the question is how to do that," National Incident Commander Thad Allen told reporters.

"I'd like to give you a definitive answer," he added, "but it's a work in progress."

BP had thought the mud and cement pumped in from above the leak may have essentially killed the well. But the relief well will allow engineers to pump in mud and cement from below in a "bottom kill" attempt to permanently seal the well.

Work on the wells was stopped this week because of bad weather.

The decision to resume work on the relief wells means a key milestone in the crisis that wreaked havoc on the Gulf Coast's economy and ecosystem remains several days off.

However, Allen has repeatedly insisted on an "overabundance of caution" when it comes to permanently plugging the well.

Pressure tests completed late on Thursday showed that the well is effectively sealed, with "no communication with the reservoir," Allen said.

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But engineers are worried that increased pressure from the "bottom kill" could damage the existing temporary cement plug and perhaps cause about 1,000 barrels of oil trapped in the well shaft to flow into the ocean, Allen said. Engineers are developing procedures to allay such concerns, he said.

After Allen gives the order to continue with the relief well, it will take about 96 hours to drill into the Macondo well shaft and perhaps days beyond that to complete the job, he said. 

On Thursday, Allen had said it was possible that the "bottom kill" would not be necessary.

It would have been difficult to say the "bottom kill" was unnecessary after promising it for weeks as the ultimate solution, said Eric Smith, associate director of the Tulane Energy Institute.

"That's been the mantra all along, that they wanted to do the bottom kill," he said.

Proceeding with the relief well makes sense, said Bob Bea, a petroleum engineering professor at the University of California, Berkeley, who is conducting his own investigation into the disaster.

Too little is known about how much cement might be inside the space between the inner piping and outer casing to be confident the well is permanently plugged, he said.

"Everything we know at this time says we need to continue the work with the relief wells," he said. "We don't know the details of how they plugged the well from the top. We don't know the volume of material they put in the well bore, and without that we can't tell how close to the bottom of the well they got."

Drilling of the first relief well began in early May. Since then, the drill has been guided some three miles from the surface and two miles beneath the sea floor to within 30 to 50 feet of the target. The drill is about as wide as a grapefruit, its target less than half the size of a dartboard.

It's unclear when the drilling could be finished. Officials had projected as early as Friday before the nasty weather forced the operation to a halt. Drilling that final stretch is a time-consuming and careful process as engineers work to make sure they don't miss.

Crews dig about 20 to 30 feet at a time, then run electric current through the relief well. The current creates a magnetic field in the pipe of the blown-out well, allowing engineers to calculate exactly where and how far they need to drill.

The flow of oil into the Gulf has been halted since July 15, when a temporary cap over the well was able to contain the spill. But officials have stressed for weeks that only a bottom kill will ensure the well is no longer a danger.

Before July 15, the oil leaked almost unimpeded for nearly three months and spewed some 206 million gallons of oil, according to the government's latest estimate. The crisis began on April 20, after an explosion on the BP PLC-leased Deepwater Horizon drilling rig that killed 11 workers. Officials don't yet know the cause of the explosion, or why machinery designed to prevent the unchecked flow of oil failed to work.

BP has already spent $6.1 billion responding to the spill.

The Associated Press and Reuters contributed to this report.

Video: BP: 'Bottom kill' threatens to expel trapped oil

Interactive: Strategies used against busted well

Photos: Month 4

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  1. The Blue Dolphin, left, and the HOS Centerline, the ships supplying the mud for the static kill operation on the Helix Q4000, are seen delivering mud through hoses at the site of the Deepwater Horizon Oil Spill in the Gulf of Mexico, off the coast of Louisiana, on Aug. 3, 2010. In the background is the Development Driller III, which is drilling the primary relief well. (Gerald Herbert / AP) Back to slideshow navigation
  2. Eddie Forsythe and Don Rorabough dump a box of blue crabs onto a sorting table at B.K. Seafood in Yscloskey, La., on Aug. 3, 2010. The crabs were caught by fisherman Garet Mones. Commercial and recreational fishing has resumed, with some restrictions in areas that were closed by the Deepwater Horizon oil spill. (Chuck Cook / AP) Back to slideshow navigation
  3. Sea turtle hatchlings that emerged from eggs gathered on the northern Gulf Coast of Florida are released at Playalinda Beach on the Canaveral National Seashore near Titusville, Fla., on Aug. 2, 2010. The sea turtles were born at a Kennedy Space Center incubation site, where thousands of eggs collected from Florida and Alabama beaches along the Gulf of Mexico have been sent. (Craig Rubadoux / Florida Today via AP) Back to slideshow navigation
  4. A crab, covered with oil, walks along an oil absorbent boom near roso-cane reeds at the South Pass of the Mississippi River in Plaquemines Parish, Louisiana on Aug. 1, 2010. BP is testing the well to see if it can withstand a "static kill" which would close the well permanently. (Pool / Reuters) Back to slideshow navigation
  5. A boat motors through a sunset oil sheen off East Grand Terre Island, where the Gulf of Mexico meets Barataria Bay on the La. coast, on the evening of July 31. (Gerald Herbert / AP) Back to slideshow navigation
  6. Oil approaches a line of barges and boom positioned to protect East Grand Terre Island, partially seen at top right, on July 31. (Gerald Herbert / AP) Back to slideshow navigation
  7. Oil from the Deepwater Horizon oil spill is seen near an unprotected island in the Gulf of Mexico near Timbalier Bay, off the coast of Louisiana on Wednesday, July 28. (Gerald Herbert / AP) Back to slideshow navigation
  8. Greenpeace activists stand outside a BP gas station in London, England, on July 27 after they put up a fence to cut off access. Several dozen BP stations in London were temporarily shut down to protest the Gulf spill. (Leon Neal / AFP - Getty Images) Back to slideshow navigation
  9. James Wilson sells T-shirts to those arriving in Grand Isle, La., for the music festival Island Aid 2010 on July 24. (Dave Martin / AP) Back to slideshow navigation
  10. Activists covered in food coloring made to look like oil protest BP's Gulf oil spill in Mexico City on July 22. The sign at far left reads in Spanish "Petroleum kills animals." (Alexandre Meneghini / AP) Back to slideshow navigation
  11. People in Lafayette, La., wear "Keep Drilling" tee shirts at the "Rally for Economic Survival" opposing the federal ban on deepwater drilling in the Gulf of Mexico on Wednesday, July 21. Supporters at the rally want President Obama to lift the moratorium immediately to protect Louisiana's jobs and economy. (Ann Heisenfelt / EPA) Back to slideshow navigation
  12. A flock of white ibis lift off from marsh grass on Dry Bread Island in St. Bernard Parish, La., July 21. Crews found about 130 dead birds and 15 live birds affected by oil from the Deepwater Horizon oil spill on July 19 in the eastern part of the parish behind the Chandeleur Islands. (Patrick Semansky / AP) Back to slideshow navigation
  13. Kenneth Feinberg, administrator of the BP Oil Spill Victim Compensation Fund testifies during a hearing before the House Judiciary Committee on July 21 in Washington, D.C. The hearing was to examine the claim process for victims of the Gulf Coast oil spill. (Alex Wong / Getty Images) Back to slideshow navigation
  14. An American white pelican has its wings checked during a physical examination at Brookfield Zoo’s Animal Hospital by Michael Adkesson and Michael O’Neill on July 21. The bird, along with four other pelicans, was rescued from the Gulf Coast oil spill and will be placed on permanent exhibit at the zoo. (Jim Schulz / Chicago Zoological Society via AP) Back to slideshow navigation
  15. Native people of the Gwich'in Nation form a human banner on the banks of the Porcupine River near Ft. Yukon, Alaska July 21, in regard to the BP oil spill with a message to protect the Arctic National Wildlife Refuge from oil development. The images include a Porcupine caribou antler and a threatened Yukon River Salmon. (Camila Roy / Spectral Q via Reuters) Back to slideshow navigation
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  1. Image:
    Gerald Herbert / AP
    Above: Slideshow (15) Oil spill disaster in the Gulf - Month 4
  2. Image: Economic And Environmental Impact Of Gulf Oil Spill Deepens
    Mario Tama / Getty Images
    Slideshow (64) Oil spill disaster in the Gulf - Month 3
  3. Image: Oil Spill In The Gulf
    Digitalglobe / Getty Images Contributor
    Slideshow (81) Oil spill disaster in the Gulf - Month 2
  4. Image: Dispersed oil caught in the wake of a transport boat floats on the Gulf of Mexico
    Hans Deryk / Reuters
    Slideshow (53) Oil spill disaster in the Gulf - Month 1
  5. Image:
    Gerald Herbert / AP
    Slideshow (10) Oil spill disaster in the Gulf - Rig explosion

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