BP links Deepwater Horizon disaster to "bad cement job"
8 Sep 2010
London – Shoddy work, materials and management practices were the likely, basic causes of the Deepwater Horizon disaster, according to BP’s report into the 20 April explosion and fire on the oil rig, which killed 11 people and caused massive pollution in the Gulf of Mexico.
“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,” said Tony Hayward, BP’s outgoing chief executive, who lost his job as a result of the accident.
However, the failings at the workface of the deep sea Macondo well were themselves the result of “a complex and interlinked series of mechanical failures, human judgements, engineering design, operational implementation and team interfaces,” said the report.
There was a sequence of failures involving a number of different parties, and decisions made by several companies and work teams, said the report. These conclusion were 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.
The BP report listed the main causes of the accident as:
- 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,” said Hayward. “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.”
The CEO added that it was unlikely that the well design contributed to the incident, noting that the investigation found that the hydrocarbons flowed up the production casing through the bottom of the well.
BP’s findings cut little ice with rig owner Transocean, the Swiss group responding with a strongly worded statement: “This is a self-serving report that attempts to conceal the critical factor that set the stage for the Macondo incident: BP’s fatally flawed well design. ’In both its design and construction, BP made a series of cost-saving decisions that increased risk - in some cases, severely.”
Meanwhile, BP’s incoming chief executive Bob Dudley said: ” We will be undertaking a broad-scale review to further improve the safety of our operations. We will invest whatever it takes to achieve that. It will be incumbent on everyone at BP to embrace and implement the changes necessary to ensure that a tragedy like this can never happen again.”
The investigation team has proposed a total of 25 recommendations designed to prevent a recurrence of such an accident. These are focused on improving the reliability of blow-out preventers, well control, pressure-testing for well integrity, emergency systems, cement testing, rig audit and verification, and personnel competence.
BP expects that 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.
The company noted 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 ongoing US government investigations.
