Houston - With a final shot of cement, BP permanently "killed" its deep-sea well in the Gulf of Mexico that ruptured in April and unleashed the worst oil spill in US history, the top US spill official said on Sunday.
"We can finally announce that the Macondo 252 well is effectively dead," retired Coast Guard Admiral Thad Allen, who oversees the US government response to the disaster, said in a statement.
"After months of extensive operations, planning and execution under the direction and authority of the U.S. government science and engineering teams, BP has successfully completed the relief well by intersecting and cementing the well nearly 18 000 feet (5.5 km) below the surface," Allen said.
President Barack Obama, whose public approval ratings were hurt by public discontent over the US government's initial response to the spill, welcomed the long-awaited development as an "important milestone".
Obama said his administration was now focused on making sure the Gulf Coast "recovers fully from this disaster".
"This road will not be easy, but we will continue to work closely with the people of the Gulf to rebuild their livelihoods and restore the environment that supports them," Obama said in a statement.
On Thursday, a relief well bored into the bottom of the Macondo well to pump in cement and seal the reservoir for good. BP pumped cement for seven hours on Friday, and finished a pressure test early on Sunday that showed the well was dead, Allen said.
The development provided an anticlimactic end to the disaster nearly five months after the well ruptured on April 20, causing an explosion aboard the Deepwater Horizon drilling rig that killed 11 workers and spewed more than 4 million barrels of oil into the sea.
The spill marred the coasts of four US Gulf states, prompted a ban on new deepwater drilling and left BP's image in tatters in the United States, home to 40% of the London-based oil giant's business.
The disaster also wiped about $70bn from BP's market value and spurred BP to replace its gaffe-prone Chief Executive Tony Hayward with an American, Bob Dudley, effective October 1.
Oil has not leaked into the sea from the mile-deep (1.6 km deep) well since BP engineers sealed it on July 15 with a cap. The well had gushed more than 16 times as much as the 257 000 barrels of oil spilled by the Exxon Valdez disaster in Alaska in 1989.
Allen said the US Department of the Interior's Bureau of Ocean Energy Management "confirmed that the cementing operation on the Macondo well was successful, that the well has been permanently sealed with cement plugs, and that pressure tests verify the integrity of the plugs."
Allen said additional regulatory steps to plug and abandon the well remain on tap "but we can now state, definitively, that the Macondo well poses no continuing threat to the Gulf of Mexico."
BP had already pumped cement into the well from the top on August 5 that provided the first cement plug. The second round into the bottom through the relief well was considered the final assurance that the well was plugged for good.