WASHINGTON — A relief well that government officials say will finally finish off BP's Deepwater Horizon well in the Gulf of Mexico won't be completed until after Labor Day, weeks later than officials had been predicting.
The delay is necessary in part because officials want to preserve the blowout preventer currently sitting atop the BP well as possible evidence in federal investigations into what caused the well to explode on April 20, retired Coast Guard Adm. Thad Allen said Thursday. That means the old blowout preventer will have to be removed and a new one set in place before engineers can complete the relief well. That process and associated tests will take at least three weeks, Allen said.
"We do not want to have damage to the blowout preventer," Allen said in explaining the delay. "We are concerned about preserving evidence."
Why the blowout preventer — a giant collection of valves designed to sever a deepwater well's drilling pipe in the event of an emergency — didn't work has been a key question for investigators. BP officials told Congress in May that diagrams they had of the blowout preventer were inaccurate and that they wasted days trying to activate its shearing mechanisms in vain. The blowout preventer is actually owned by Transocean, the rig operator from which BP had leased the Deepwater Horizon drilling rig. BP and Transocean have blamed one another for the blowut preventer's failure to seal the well.
An order Allen issued to BP Thursday authorizing the replacement of the blowout preventer specified that "each precedure should recognize and preserve the forensic and evidentiary value of the BOP and any material removed from the BOP."
Allen has emphasized for weeks that the Obama administration will not consider the BP well dead until the relief well is completed and heavy drilling mud and cement have been pumped into the well's annulus, the space between the well's drill pipe and the wall of the wellbore.
Previously, Allen had said he believed crews would be ready to intercept the Deepwater Horizon well in mid August. The relief well was begun on May 2 and currently is about three and a half feet horizonally from the Deepwater Horizon wellbore and about 50 feet vertically from the point where engineers hope to make the intercept.
That operation, however, has become less urgent in the wake of two key events: the successful sealing of a containment cap above the blowout preventer July 15, which cut off the flow of crude oil into the Gulf, and the successful "static kill" of the well earlier in August, when heavy drilling mud poured into the well forced oil in the well back into the reservoir 18,000 feet below the sea's surface. That was followed with cement.
Officials have said repeatedly since then that there is no oil seeping out of the reservoir into the drill pipe or the annulus, and the Obama administration has gone so far as to declare that three-quarters of the oil that had escaped from the well has been dispersed or evaporated.
But Allen said Thursday that engineers still are uncertain why the well appears to be sealed and that some government scientists fear that a blockage between the reservoir and the well's annulus may be simply the result of a collapse of rock formations and not a permanent seal with cement.
Easing those fears by placing cement in the annulus via the relief well raised new risks of undoing the seals already in place, however, and Allen said the delay in completing the relief well will allow BP to undertake a series of steps to lessen that danger.
The first, Allen said, would be to remove any drilling mud and cement from the current blowout preventer and containment cap and replace it with much lighter seawater. That process has already begun, with BP reconnecting a drill ship on the surface to the containment cap to capture the drilling mud and crude oil.
Technicians will then monitor the well for 48 hours before undertaking what Allen called a "fishing experiment" to remove the well's drill pipe from the blowout preventer. That steps, Allen said, is necesssary to make certain that moving the blowout preventer doesn't damage the 5,000 feet of cement currently sealing the well.
Finally, a new blowout preventer will be brought in to replace the old one. Preparing the old blowout preventer for removal and testing the new one, in addition to the other steps, "takes you to after Labor Day," Allen said.
Allen said the new plan had been the subject of "intense negotiations" in recent days between BP officials and the Obama administration, including Secretary of Energy Steven Chu. Allen did not specify what the points of contention had been, however.