BP starts flushing Macondo subsea equipment before pressure tests

Paula Dittrick
OGJ Senior Staff Writer

HOUSTON, Aug. 19 -- BP PLC has started preparations to flush drilling mud and hydrocarbons from the deepwater Macondo well sealing cap and the Deepwater Horizon’s lower marine riser package (LMRP) and blowout preventer (BOP) in the Gulf of Mexico.

The flush is needed before BP conducts a pressure test to study the well's BOP stack and sealing cap under ambient conditions, National Incident Commander and retired US Coast Guard Adm. Thad Allen said Aug. 18.

“This will be one of the final vital signs that we will need in order to make a determination on how to go forward,” Allen said of plans to drill into the annulus of the Macondo well using a relief well. On Aug. 19, he said the tentative plan is to replace the Deepwater Horizon BOP before doing the bottom kill. A final decision depends upon pressure test results. 

He estimated the relief well's intervention of the Macondo well could take place the week after Labor Day.

BP also plans a "fishing experiment" to find drill pipe and other material that might interfere with the BOP replacement, Allen said. "Each procedure should recognize and preserve the forensic and evidentiary value of the BOP and any material removed from the BOP."

An Apr. 20 blowout of the Macondo well, being drilled by Transocean Ltd.’s Deepwater Horizon semi for BP and partners, caused a fire and explosion, killing 11 people and resulting in an oil spill that a federal science team estimates at 4.9 million bbl from the well.

“We are concerned that a pressure going up the annulus could push through a seal at the top, enter the blowout preventer in the capping stack, and might cause a problem to the existing combination of the Deepwater Horizon blowout preventer and the capping stack that's been installed and the connecting spool that joins them together,” Allen said. BP estimates 1,000 bbl of oil could be in the annulus.

As part of the flushing procedure, Transocean’s Discoverer Enterprise plans to attach drillstring to the top of the sealing cap. Crews will open the middle blind shears of the sealing cap. The Helix Q4000 will pump an antifreeze mixture through the existing seabed manifold into the BOP's choke and kill lines.

The liquid used in the flushing will be completely contained and carried to the surface through the Enterprise drillstring. After the flush is completed, the sealing cap's blind shear ram will be closed, BP said.

Following the flush, BP will conduct an ambient pressure test to reassure that the well is secure. The test will be conducted over 48-hr, which is twice the time that BP estimates it would take to remove the failed Deepwater Horizon BOP and replace it with the Transocean Development Driller II BOP.

The DDII is preparing its BOP for use on the Macondo wellhead. Drilling crews will set a storm packer will in the second relief well before moving off the drilling site.

The second relief well was started as a backup to the first relief well. The DDII has been on hold for weeks pending completion of the first relief well, which is being drilled by Transocean’s Development Driller III.

Contact Paula Dittrick at paulad@ogjonline.com.

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