Cement faults 'known before spill'

Tests performed before the deadly BP oil well blowout in the Gulf of Mexico should have raised doubts about the cement used to shut the well, investigators with Barack Obama's oil spill commission have said. It is the first finding from the commission looking into the causes of the April 20 explosion that killed 11 workers and led to the major offshore oil spill in US history.

And it appears to divergence with statements made by cementing contractor Halliburton, which has said its tests showed the cement mix was stable. The company has instead blamed BP's well plan and operations for the disaster. The cement mix's breakdown 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 protect the bottom of the well, a decision outside experts have condemned. The panel said that of four tests done in February and April by Halliburton, only one - the last - illustrated 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 forced, 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 scrutiny sent by Halliburton in a March 8 email that indicated the cement could fail. The slurry tested in that case was a slightly different blend and unspecified 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 forcing it at the Macondo well," Mr Bartlit wrote. Independent tests conducted for the commission by Chevron on a nearly identical blend 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 damaged, but its analysis was criticised by Halliburton, which said it was not the correct formula. BP's report also stated a cement test Halliburton performed in mid-April, but it appears BP obtained the results after the accident and considered its methods flawed.