Washington (CNN) -- Oil giant BP and contractor Halliburton knew of potential flaws in the cement slurry used to reinforce the oil well below the Deepwater Horizon rig before it exploded in April, according to a letter Thursday from the lead investigator for a federal probe of the Gulf oil disaster.
The letter from Fred Bartlit Jr. to the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling said that tests in February on a cement slurry similar to what was used on the Macondo well showed instability -- and that both companies had the data.
According to Bartlit's letter, the cement was poured to stabilize the well on April 19 and 20. The 20th was the day of the explosion on the Deepwater Horizon rig above the well that killed 11 workers and caused the worst oil spill in U.S. history.
"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.
"Halliburton (and perhaps BP) should have considered redesigning the foam slurry before pumping it at the Macondo well," the letter continued.
The news caused Halliburton stock to drop in value by almost 8 percent by the end of trading Thursday, to $31.68 a share. U.S. Rep. Edward Markey, D-Massachusetts, called for the oil spill commission to get full subpoena power, and for BP CEO Bob Dudley to agree to testify before Congress.
CNN
