Crews to protect Macondo casing hanger during BOP swap

The casing hanger and annulus seal have taken center stage in BP PLC’s plan to replace the Transocean Ltd. Deepwater Horizon semisubmersible's blowout preventer with another blowout preventer.

Engineers and scientists calculated 80,000 pounds of force can be used to pull the Deepwater Horizon BOP off the blown-out Macondo well. National Incident Commander and US Coast Guard Adm. Thad Allen describes this as “a gentle tug.”

“What they’re concerned about is somehow potentially dislodging the casing hanger that is at the top of the well,” Allen said.

An earlier ambient pressure test indicated a static condition in the annulus, Allen said. This situation gives crews the confidence that they can change out the BOP without causing any harm before proceeding with completion of the relief well.

“What we’re trying not to do is create some change to the static situation in relation to the seals that are keeping the annulus at a static condition as we try and lift the blowout preventer up,” Allen said. “That’s the reason there’s a limit to how much pull we’re using.”

The casing hanger is part of a subsea wellhead system built by Dril-Quip of Houston.