The letter released Thursday by the staff of the National Commission on the BP Deepwater Horizon Oil Spill indicates that Halliburton conducted four tests of the foam cement used to prevent natural gas or oil from flowing up the BP Macondo well. Three of the four indicated the cement would be unstable.
In a March 8, 2010, memo, Halliburton shared data with BP about one of two tests conducted in February. The test indicated the cement formula would be unstable, but there was no evidence that Halliburton highlighted the issue as a problem or that BP personnel asked questions, investigators for the commission found, according to the letter. The data was included in a technical report along with other information.
"Halliburton and BP both had results in March showing that a very similar foam slurry design to the one actually pumped at the Macondo well would be unstable, but neither acted upon that data," the letter said.
Two more tests of the cement formula were conducted in April, the commission staff found. One indicated the foam cement would be unstable, but may have been done improperly. The second indicated the cement would work properly.
"We are not yet certain when Halliburton reported this data internally or whether the test was even complete prior to the time the cement job was poured" at the BP Macondo well, the commission staff wrote.
"Halliburton (and perhaps BP) should have considered redesigning the foam slurry before pumping it at the Macondo well," concluded the spill commission's chief counsel, Fred Bartlit, and other staffers in a letter sent on Thursday to the commission.
Halliburton spokeswoman Cathy Mann said the company would review the commission's report and respond later Thursday.
BP did not immediately respond to a request for comment.
The Deepwater Horizon exploded on April 20, killing 11 workers. Oil poured from the broken well for weeks while BP, federal officials and contractors struggled to cap and permanently seal the well. The spill became an acute political problem for the Obama administration, and led the administration to declare a halt to new deep-water drilling that was only lifted earlier this month.
The spill commission's questions about the cementing job will likely revive fingerpointing among the companies responsible for the Deepwater Horizon's operations.
The new information reflects the results of four Halliburton foam-stability tests, two conducted in February 2010 and two conducted in April 2010.
The first two tests—using a slightly different cement slurry design from that used in the Macondo well—indicated that the foam-slurry design was unstable, the letter from the spill commission staff said.
Of the second two tests—this time using the actual recipe and design of the cement poured at the Macondo well—the first test indicated that the foam slurry design was unstable, according to the letter. The final test—conducted using a modified testing procedure—showed that the foam would be stable, the letter said.
"Taken together, these documents lead us to believe that only one of the four tests discussed above that Halliburton ran on the various slurry designs for the final cement job at the Macondo well indicated that the slurry design would be stable," according to the letter.
But "Halliburton may not have had—and BP did not have—the results of that test before the evening of April 19, meaning that the cement job may have been pumped without any lab results indicating that the foam cement slurry would be stable," according to the letter.
Halliburton provided data from one of the two February tests to BP in a March 8 email, according to the letter. But the data appeared in a technical report along with other information. "There is no indication that Halliburton highlighted to BP the significance of the foam stability data or that BP personnel raised any questions about it."
In September, BP concluded that the nitrogen-cement mix likely didn't hold, based on testing conducted by CSI Technologies in Houston. But the lab had to test a foam similar to that used in the Macondo well because Halliburton declined to provide a similar cement mixture.
On Thursday, the spill commission said that it had asked Chevron Corp. to conduct another test, this time based on off-the-shelf cement and additives used at the Macondo well that Halliburton had in stock. Chevron's lab personnel "were unable to generate stable foam cement in the laboratory using the materials provided by Halliburton and the available design information.
"Although laboratory foam stability tests cannot replicate field conditions perfectly, these data strongly suggest that the foam cement used at Macondo was unstable," according to the letter. "This may have contributed to the blowout."