BP said its own engineers, rig operator Transocean and contractor Halliburton share part of the blame for the explosions on the Deepwater Horizon rig that resulted in the deaths of 11 people and a massive oil spill in the Gulf of Mexico.
BP's 4-month internal investigation into the disaster came to the conclusion that a sequence of equipment and human judgment errors led to the worst oil spill in the history of the United States.
Compiled by more than 50 engineers and specialists who reported to Mark Bly, BP's chief of safety, the report was released Wednesday on the company's Web site.
It tries to reconstruct the events of April 20, when natural gas erupted from the subsea Macondo well, shot up through the rig and onto the platform, igniting a series of explosions that killed 11 people and resulted in the sinking of the platform. For the next 3 months, despite several attempts by BP to seal the well, it continued to spew crude into the gulf, devastating ocean wildlife and the regional economy.
BP says "a complex and interlinked series of mechanical failures, human judgments, engineering design, operational implementation and team interfaces came together to allow the initiation and escalation of the accident. Multiple companies, work teams and circumstances were involved over time."
It lists the following failures:
-- Two cement barriers at the bottom of the well failed to isolate hydrocarbons within the reservoir, instead allowing the crude to flow up the well. BP says Halliburton's faulty cement is at least partly responsible for that.
-- BP and Transocean staff incorrectly accepted the results of a negative pressure test, conducted April 20 to establish whether the well holds tight. The test revealed abnormally high pressure in the well but the crew attributed it to the so-called bladder effect -- a tragic misinterpretation, the report reveals.
By then, hydrocarbons entered and rose up the well, which should have been sealed. Over a period of 40 minutes, hydrocarbons rose, with the pressure increasing despite the fact that the pumps were off -- a clear red flag that was either ignored or not detected by the Transocean crew, BP says.
-- When crew members reacted, the situation was almost too late. They might have prevented the disaster by diverting the rapidly rising hydrocarbons overboard. Instead, the crew decided to route them to a mud-gas separator, designed to hold only limited amounts of gas. The system was soon overwhelmed, with gas flowing directly onto the rig and igniting a series of explosions.
-- The fire and gas emergency system should have prevented those explosions but it didn't.
-- Even after the explosions and the fire had started, a blow-out preventer system on the seabed should have automatically sealed the well but it also failed to operate.
BP said it's unlikely that its well design was to blame for the accident. Other oil companies criticized BP for using a well design that was cheaper but less safe that traditional ones.
Transocean and Halliburton have yet to comment on the report.
Bly, who led the investigation, said the report was designed not to attribute blame but to identify the key elements behind the disaster to prevent similar ones from happening again. The report lists 25 recommendations put to the BP management to improve drilling safety.
Bob Dudley, BP's new U.S. chief executive officer, in a statement said the company was "determined to learn the lessons for the future."
BP's market value dropped nearly 40 percent in the aftermath of the disaster, which also led to the sacking of former CEO Tony Hayward.
The publication of the report comes as other investigations continue, including the U.S. Justice Department's criminal probe.
BP's 4-month internal investigation into the disaster came to the conclusion that a sequence of equipment and human judgment errors led to the worst oil spill in the history of the United States.
Compiled by more than 50 engineers and specialists who reported to Mark Bly, BP's chief of safety, the report was released Wednesday on the company's Web site.
It tries to reconstruct the events of April 20, when natural gas erupted from the subsea Macondo well, shot up through the rig and onto the platform, igniting a series of explosions that killed 11 people and resulted in the sinking of the platform. For the next 3 months, despite several attempts by BP to seal the well, it continued to spew crude into the gulf, devastating ocean wildlife and the regional economy.
BP says "a complex and interlinked series of mechanical failures, human judgments, engineering design, operational implementation and team interfaces came together to allow the initiation and escalation of the accident. Multiple companies, work teams and circumstances were involved over time."
It lists the following failures:
-- Two cement barriers at the bottom of the well failed to isolate hydrocarbons within the reservoir, instead allowing the crude to flow up the well. BP says Halliburton's faulty cement is at least partly responsible for that.
-- BP and Transocean staff incorrectly accepted the results of a negative pressure test, conducted April 20 to establish whether the well holds tight. The test revealed abnormally high pressure in the well but the crew attributed it to the so-called bladder effect -- a tragic misinterpretation, the report reveals.
By then, hydrocarbons entered and rose up the well, which should have been sealed. Over a period of 40 minutes, hydrocarbons rose, with the pressure increasing despite the fact that the pumps were off -- a clear red flag that was either ignored or not detected by the Transocean crew, BP says.
-- When crew members reacted, the situation was almost too late. They might have prevented the disaster by diverting the rapidly rising hydrocarbons overboard. Instead, the crew decided to route them to a mud-gas separator, designed to hold only limited amounts of gas. The system was soon overwhelmed, with gas flowing directly onto the rig and igniting a series of explosions.
-- The fire and gas emergency system should have prevented those explosions but it didn't.
-- Even after the explosions and the fire had started, a blow-out preventer system on the seabed should have automatically sealed the well but it also failed to operate.
BP said it's unlikely that its well design was to blame for the accident. Other oil companies criticized BP for using a well design that was cheaper but less safe that traditional ones.
Transocean and Halliburton have yet to comment on the report.
Bly, who led the investigation, said the report was designed not to attribute blame but to identify the key elements behind the disaster to prevent similar ones from happening again. The report lists 25 recommendations put to the BP management to improve drilling safety.
Bob Dudley, BP's new U.S. chief executive officer, in a statement said the company was "determined to learn the lessons for the future."
BP's market value dropped nearly 40 percent in the aftermath of the disaster, which also led to the sacking of former CEO Tony Hayward.
The publication of the report comes as other investigations continue, including the U.S. Justice Department's criminal probe.
