No single factor caused the Macondo well tragedy, according to BP. Rather, a sequence of failures involving a number of different parties led to the explosion and fire which killed 11 people and caused widespread pollution in the Gulf of Mexico earlier this year.
A report released by BP today concludes that decisions made by ‘multiple companies and work teams’ contributed to the accident which it says arose from ‘a complex and interlinked series of mechanical failures, human judgments, engineering design, operational implementation and team interfaces’.
The report – based on a four-month investigation led by Mark Bly, BP’s head of safety and operations and conducted independently by a team of over 50 technical and other specialists drawn from inside BP and externally – found that:
* The cement and shoe track barriers – and in particular the cement slurry that was used – at the bottom of the Macondo well failed to contain hydrocarbons within the reservoir, as they were designed to do, and allowed gas and liquids to flow up the production casing;
* The results of the negative pressure test were incorrectly accepted by BP and Transocean, although well integrity had not been established;
* Over a 40-minute period, the Transocean rig crew failed to recognise and act on the influx of hydrocarbons into the well until the hydrocarbons were in the riser and rapidly flowing to the surface;
* After the well-flow reached the rig it was routed to a mud-gas separator, causing gas to be vented directly on to the rig rather than being diverted overboard;
* The flow of gas into the engine rooms through the ventilation system created a potential for ignition which the rig’s fire and gas system did not prevent;
* Even after explosion and fire had disabled its crew-operated controls, the rig’s blow-out preventer on the sea-bed should have activated automatically to seal the well. But it failed to operate, probably because critical components were not working.
“The investigation report provides critical new information on the causes of this terrible accident. It is evident that a series of complex events, rather than a single mistake or failure, led to the tragedy. Multiple parties, including BP, Halliburton and Transocean, were involved,” comments BP’s outgoing chief executive Tony Hayward.
“To put it simply, there was a bad cement job and a failure of the shoe track barrier at the bottom of the well, which let hydrocarbons from the reservoir into the production casing. The negative pressure test was accepted when it should not have been, there were failures in well control procedures and in the blow-out preventer; and the rig’s fire and gas system did not prevent ignition.”
He continues: “Based on the report, it would appear unlikely that the well design contributed to the incident, as the investigation found that the hydrocarbons flowed up the production casing through the bottom of the well.”
BP’s incoming chief executive Bob Dudley says: “We have said from the beginning that the explosion on the Deepwater Horizon was a shared responsibility among many entities. This report makes that conclusion even clearer, presenting a detailed analysis of the facts and recommendations for improvement both for BP and the other parties involved. We have accepted all the recommendations and are examining how best to implement them across our drilling operations worldwide.”
BP says it expected a number of the investigation report’s findings to be considered relevant to the oil industry more generally and for some of the recommendations to be widely adopted.
BP notes that additional relevant information may be forthcoming, for example, when Halliburton’s samples of the cement used in the well are released for testing and when the rig’s blow-out preventer is fully examined now that it has been recovered from the sea-bed. There will also be additional information from the multiple ongoing US government investigations.