Contractor Halliburton has admitted that it skipped a crucial test on the final formulation of cement used to seal the BP oil well that blew out in the Gulf of Mexico.
The company, which was BP’s cementing contractor, said that BP at the last minute increased the amount of a critical ingredient in the cement mix.
While an earlier test showed the cement was stable, the company never performed a stability test on the new blend.
The cement’s failure to prevent oil and gas from entering the Deepwater Horizon well has been identified as one of the causes of the 20 April disaster which killed 11 workers and led to the largest offshore oil spill in US history.
Halliburton made the admission in a six-page statement issued in response to findings by US president Barack Obama’s oil spill commission.
Commission investigators said last night that tests performed before the deadly blowout should have raised doubts about the cement used to seal the well.
It was the first finding from the commission looking into the causes of the explosion.
That appeared to conflict with earlier statements made by Halliburton, which said its tests showed the cement mix was stable. The company instead blamed BP’s well design and operations for the disaster.
The cement mix’s failure to prevent oil and gas from entering the well has been identified by BP and others as one of the causes of the accident.
BP and Halliburton decided to use a foam slurry created by injecting nitrogen into cement to secure the bottom of the well, a decision outside experts have criticised.
The panel said that of four tests done in February and April by Halliburton, only one – the last – showed the mix would hold. But the results of that single successful test were not shared with BP and may not have reached Halliburton before the cement was pumped, according to a letter sent to commissioners by chief investigative counsel Fred Bartlit.
BP had at the time of the blowout the results of only one of the tests – a February analysis sent by Halliburton in a 8 March email that indicated the cement could fail.
The slurry tested in that case was a slightly different blend and assumed a slightly different well design, but there was no indication that Halliburton flagged the problem for BP, or that BP had concerns, the letter said.
“Halliburton (and perhaps BP) should have considered redesigning the foam slurry before pumping it at the Macondo well,” Bartlit wrote.
Independent tests conducted for the commission by Chevron on a nearly identical mixture were also released. The results concluded that the cement mix was unstable, raising questions about the validity of Halliburton’s final test.
BP, as part of its internal investigation, also conducted independent tests that showed the cement mix was flawed, but its analysis was criticised by Halliburton, which said it was not the correct formula. BP’s report also mentioned a cement test Halliburton performed in mid-April, but it appears BP obtained the results after the accident and considered its methods flawed.
By contrast, the commission obtained proprietary additives from Halliburton as well as a recipe to recreate the slurry that was used on the well. One and a half gallons of the actual mix used on the rig remain, but it is being held as evidence in criminal and civil investigations.
In evidence before the joint Coast Guard-Bureau of Ocean Energy Management investigative panel, Halliburton engineer Jesse Gagliano, when asked if he would pour the same cement again, said he would.
“I am comfortable with the slurry design,” he said.
The independent investigators do not address other decisions that could have contributed to the cement’s failure, such as BP’s decision to use fewer centralisers than recommended by Halliburton. Centralisers make sure the well’s piping is centred inside the well so the cement bonds correctly.
BP has also been criticised for not performing a cement bond log, a test that checks after the cement is pumped down whether it is secure. There are also questions about whether BP pumped down enough cement to seal off the bottom of the well, which was located more than 4km below sea level.