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BP did not properly communicate to the drill crew the lack of testing on the cement or the uncertainty surrounding critical tests and procedures used to confirm the integrity of the barriers intended to inhibit the flow of hydrocarbons from the well. A hydrocarbon is a compound consisting of hydrogen and carbon that is found in oil and gas.

BP adopted a technically complex nitrogen foam cement program for sealing the well. The resulting cementing job was of minimal quantity, left little margin for error, and was not tested adequately before or after the cementing operation. Further, the integrity of the cement may have been compromised by contamination, instability, and an inadequate number of devices used to center the casing in the wellbore.

—Cement contractor Halliburton and BP did not adequately test the cement slurry used to seal the well.

BP also failed to assess the risk of the temporary abandonment procedure used at Macondo. At the time of the explosion, BP was making sure the well was sealed so it could temporarily abandon the site and perhaps come back at some point in the future to produce oil from the exploratory well. Transocean said BP generated at least five different temporary abandonment plans for the Macondo well between April 12, 2010, and April 20, 2010. After this series of last-minute alterations, BP proceeded with a temporary abandonment plan that created risk and did not have the required government approval.

As for the 300-ton blowout preventer that failed to stop the oil from leaking, Transocean said its investigation determined that the device and its control system were fully operational at the time of the incident and functioned as designed. Its report said minor leaks identified before the incident did not adversely affect the functionality. Transocean blamed the high flow rate of hydrocarbons from the well for preventing the device from sealing on the drill pipe. Transocean, as owner of the rig, was responsible for maintaining the blowout preventer.

The official U.S. government investigation previously blamed the failure of the Cameron-made blowout preventer on a design flaw and a bent piece of pipe. It also suggested that actions taken by the Transocean rig crew during its attempts to control the well around the time of the disaster may have contributed to the piece of drill pipe getting trapped.

At least one outside expert said at the time that the government findings cast serious doubt on the reliability of all the other blowout preventers used by the drilling industry.

BP wasn’t satisfied that the official investigation conducted all of the necessary tests to determine the cause of the blowout preventer failure. It got court approval for additional testing, which has been conducted in recent weeks.

Associated Press writers Mary Foster and Kevin McGill in New Orleans contributed to this report.