Finger pointing in the Deepwater Horizon Gulf disaster will continue for a long time. So along those lines, an internal investigation by Transocean, the owner of the rig that exploded in the Gulf last year, largely blames oil giant BP for the disaster.

The Transocean report said the April 20, 2010, Deepwater Horizon explosion and resulting oil spill was the result of a succession of well design, construction, and temporary abandonment decisions that compromised the integrity of the well and compounded the risk of its failure. The Swiss firm said quite a few of those decisions came from well owner BP in the two weeks before the incident.

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Transocean said its evidence indicates BP failed to properly assess, manage and communicate risk. On one key aspect — the failure of the blowout preventer to keep oil from leaking into the sea — Transocean seemed to suggest it takes no blame.

BP’s own internal report on the disaster blamed a cascade of failures by multiple companies for the disaster. The companies involved in the disaster have sued each other seeking to recoup their losses or expected losses from the disaster.

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In addition to owning the well that blew out, London-based BP was leasing the rig that exploded from Transocean. Eleven rig workers were killed and the government estimates some 206 million gallons of oil leaked from BP’s Macondo well a mile beneath the sea before the well was capped three months later. It was the worst offshore oil spill in U.S. history, staining hundreds of miles of shoreline, hurting fisherman and businesses and prompting new rules for deepwater drilling. BP has already spent or committed tens of billions of dollars to clean up the mess and compensate victims.

The Transocean report was the culmination of work by an internal investigation team comprised of experts from various technical fields and other specialists. Transocean said the loss of evidence with the rig and the unavailability of certain witnesses limited its investigation and analysis in some areas.

Among Transocean’s findings:
• 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.
• 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 they did not test it adequately before or after the cementing operation. Further, there may have been a compromise in the integrity of the cement via 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 they sealed the well 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 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 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 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.

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