BP replaces failed blowout preventer on Gulf well

HOUSTON (Reuters) - BP Plc successfully replaced a failed blowout preventer from atop its ruptured Gulf of Mexico oil well late on Friday, the top U.S. official overseeing the spill response said.

Retired Coast Guard Admiral Thad Allen called the equipment switch "an important milestone" toward permanently killing the leak that spewed more than 4 million barrels of oil into the Gulf from April 20 through mid-July.

"During the period of time between the removal of the damaged BOP and installation of the replacement BOP, there was no observable release of hydrocarbons from the wellhead," Allen said.

The failed 50-foot (15-meter) stack of valves and pipes is critical evidence in criminal and civil investigations into the April 20 blowout that led to an explosion aboard the Deepwater Horizon drilling rig that killed 11 men.

BP replaced it with a working BOP to preserve its value as evidence and ensure working equipment sat atop the well before a relief well allows the final kill to occur.

Allen said earlier Friday that it would take 24 to 36 hours to slowly lift the failed BOP to a rig on the surface to be transported to shore. The failed BOP was removed from the wellhead early on Friday afternoon.

BP expects to resume drilling the relief well in the coming days. By mid-September the relief well is expected to bore into the ruptured Macondo well near its bottom about 13,000 feet beneath the seabed and pump in mud and cement to plug the leak for good.

BP and government officials did not expect oil to leak from the well once the failed blowout preventer was lifted off. The company pumped cement into the well from the top on August 5, which officials believe sealed off the well from the reservoir.

(Reporting by Kristen Hays, editing by Anthony Boadle)