Choppy seas delayed BP PLC's plans to retrieve the Transocean Ltd.'s Deepwater Horizon semisubmersible blowout preventer (BOP) with two pieces of pipe inside it and to install another BOP.
Plans called for the drill pipe going down into the blown-out Macondo well to be left in place, at least for now, National Incident Commander and retired Adm. Thad Allen said.
Scientists and engineers were concerned about the force that 6-8 ft waves might put on the lines that will lift the BOP off the Macondo well.
Crews calculated a safe force level for removing the BOP while avoiding damage to the well's casing hanger and seal assembly. The waves on Aug. 30 exceeded that dynamic loading factor, Allen said.
Previously, BP, operator of the Macondo well, proved unsuccessful in using a fishing operation to remove an 18-in. long pipe that was crosswise in the BOP. The 18-in. pipe was cut off from the riser while crews installed oil containment equipment on top of the BOP. A second pipe, which is about 13 ft long, also is in the BOP.
"They are fragile, and they break apart when we try to pull them out," Allen said of those two pipes. The third pipe, held suspended from the BOP, has been estimated at up to 3,500 ft long.
An Apr. 20 blowout of the Macondo well resulted in an explosion and fire on the Deepwater Horizon, killing 11 people. The Deepwater Horizon sank on Apr. 22. Macondo is on Mississippi Canyon Block 252 in 5,000 ft of water.
During an earlier "static kill" procedure, BP pumped heavy drilling mud and then cement into the casing from the top of the well following the July 15 installation of a capping stack that temporarily stopped the spill pending completion of a relief well (OGJ, Aug. 9, 2010, p. 27).
BP plans to remove a capping stack and replace the Deepwater Horizon BOP with a BOP from Transocean's Development Driller II semi, Allen said.
Transocean's Discoverer Enterprise drillship is expected to remove the capping stack, which will be placed on the seabed in case it might be needed again. The Helix Q4000 multiservice vessel then will attempt to lift the Deepwater Horizon BOP, Allen said.
If necessary, crews are prepared to use what Allen calls "a gentle tug" involving 80,000 lb of force to free the BOP. Remotely operated vehicles then will be used to cut off the drill pipe below it.
If the gentle tug fails, then BP plans to open rams in the BOP's lower marine riser package before it cuts off the pipe. Allen said BP is prepared to use tools to force open the rams.
The Department of Justice Criminal Investigation Evidence Recovery team planned to supervise the BOP replacement efforts. A team of 11 people was expected to be aboard the Helix Q4000 and Enterprise when the Deepwater Horizon BOP is lifted to the surface.
Once the Deepwater Horizon BOP is removed, the DDII will install a different BOP on the wellhead in preparation for completion of a relief well, being drilled by the Development Driller III, to kill the Macondo well using mud and cement at the bottom of the well.
Allen estimates the DDIII could resume drilling the relief well on Sept. 9-10 assuming no more delays.
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