OGJ Senior Staff Writer
HOUSTON, Sept. 1 -- BP PLC tentatively planned to remove a capping stack from the top of the Transocean Ltd.’s Deepwater Horizon semisubmersible blowout preventer on Sept. 2, pending the anticipated arrival of calmer seas in the Gulf of Mexico, a federal spokesman said.
The planned removal of the capping stack and subsequent replacement of the BOP has been on hold since Aug. 30 because of 6-ft seas caused by local weather around the mouth of the Mississippi River. Weather forecasters expect a window of calmer seas throughout Sept. 2-4.
National Incident Commander and retired US Coast Guard Adm. Thad Allen said a riser pipe from the Enterprise will be attached to the capping stack, which will be moved to the side and stored temporarily on the seabed near the Macondo well on Mississippi Canyon Block 252.
When wave levels are no more than 3 ft, the Helix Q4000 multiservice vessel will use a drillstring to remove the Deepwater Horizon BOP, Allen said.
The drillstring is not as substantial as a riser pipe, Allen said, noting that the capping stack can be removed in higher seas than can the BOP. Crews are prepared to use what Allen calls “a gentle tug” involving 80,000 lb of force to free the BOP.
Engineers and scientists calculated a limit of 80,000 lb of force to ensure the integrity of a casing hanger and an annulus seal at the top of the well, he said.
If the gentle tug fails, BP plans to open rams in the BOP’s lower marine riser package before it cuts off the drill pipe, Allen said. An estimated 3,500 ft of pipe extends down into the well, and it will be left there for now.
“Disposition of any remaining drill pipe in the well will be addressed as part of the plug and abandonment procedures that would take place after the well intercept consistent with the Bureau of Ocean Energy Management[, Regulation, and Enforcement],” Allen said.
The Deepwater Horizon BOP will be brought to the Q4000 vessel and eventually transferred to the authority federal investigators. An Apr. 20 blowout of BP’s deepwater Macondo well caused an explosion and fire on the Deepwater Horizon semisubmersible, killing 11 people.
“We will not know the exact status [of the Deepwater Horizon] BOP until we get that thing off and look at it,” Allen said.
Once the Deepwater Horizon BOP is removed, Transocean’s Development Driller II semi will install another BOP on the Macondo well so that a relief well being drilled by the Development Driller III can be completed to intercept the Macondo well and kill it from the bottom.
“We do believe the risks are small of a hydrocarbon release, but we want to be sure we are prepared for all contingencies,” Allen said. “There shouldn’t be any hydrocarbon release into the environment.”
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BP hopes to remove capping stack on Sept. 2