NEW ORLEANS (AP) - Oil giant BP PLC laid much of the blame for the rig explosion and the massive Gulf of Mexico spill on itself, other companies' workers and a complex series of failures in an internal report released Wednesday before a key piece of evidence has been analyzed.
In its 193-page report posted on its website, the British company described the incident as an accident that arose from a complex and interlinked series of mechanical failures, human judgments, engineering design, operational implementation and team interfaces.
BP spread the blame around, and even was critical of its own workers' conduct, but it defended some parts of the well's design and it was careful in its assessments. It already faces hundreds of lawsuits and billions of dollars of liabilities. In public hearings, it had already tried to shift some of the blame to rig owner Transocean Ltd. and cement contractor Halliburton. BP was leasing the rig from Transocean and owned the well that blew out.
While BP didn't completely absolve its engineers, the company shot down some of the things they've been criticized for by members of Congress and others.
"Well control actions taken prior to the explosion suggest the rig crew was not sufficiently prepared to manage an escalating well control situation," the report said.
A Transocean lawyer said the company had no immediate comment on the report.
Shares in BP extended gains after the release of the report. The stock was up 2 percent at 414.95 pence ($6.41) shortly after the report was made public Wednesday.
The report was generated by a BP team led by Mark Bly, BP's head of safety and operations.
BP's report is far from the final word on possible causes of the explosion, as several divisions of the U.S. government, including the Justice Department, Coast Guard and Bureau of Ocean Energy Management, Regulation and Enforcement, are also investigating.
Also, a key piece of the puzzle - the blowout preventer that failed to stop the oil from leaking from the well off the Louisiana coast - was raised from the water Saturday. As of Tuesday afternoon, it had not reached a NASA facility in New Orleans where government investigators planned to analyze it, so those conclusions were not be part of BP's report.
The April 20 rig explosion killed 11 workers and led to 206 million gallons of oil spewing from BP's undersea well.
Investigators know the explosion was triggered by a bubble of methane gas that escaped from the well and shot up the drill column, expanding quickly as it burst through several seals and barriers before igniting.
But they don't know exactly how or why the gas escaped. And they don't know why the blowout preventer didn't seal the well pipe at the sea bottom after the eruption, as it was supposed to.
The details of BP's internal report were closely guarded - and only a short list of people saw it ahead of its release.
There were signs of problems prior to the explosion, including an unexpected loss of fluid from a pipe known as a riser five hours before the explosion that could have indicated a leak in the blowout preventer.
Witness statements show that rig workers talked just minutes before the blowout about pressure problems in the well.
At first, nobody seemed too worried, workers have said. Then panic set in.
Workers called their bosses to report that the well was "coming in" and that they were "getting mud back." The drilling supervisor, Jason Anderson, tried to shut down the well.
It didn't work. At least two explosions turned the rig into an inferno.
Members of Congress, industry experts and workers who survived the rig explosion have accused BP's engineers of cutting corners to save time and money on a project that was 43 days and more than $20 million behind schedule at the time of the blast.
In its report, BP defended the well's design, which has been criticized by industry experts.
"The investigation team reviewed the decision to install a 9 7/8 in. x 7 in. long string production casing rather than a 7 in. production liner, which would have been tied back to the wellhead later, and concluded that both options provided a sound basis of design."
Other findings in the BP report include:
Flammable fluids rising up the pipe toward the Deepwater Horizon rig were directed to a system that allowed gas to vent onto the rig, and that gas was then circulated by the air conditioning, heating and ventilation systems. BP says that if the crew had directed the fluids overboard, there might have been more time to respond to the pending disaster and the consequences of the accident may have been reduced.
The company said the cement components for the well were stocked on Deepwater Horizon. Halliburton shipped samples of those components to its laboratory in advance of the date on which the components were used for the Macondo well. Halliburton retained surplus samples from the testing program. However, the investigation team was unable to acquire and test these actual cement samples from the rig due to a court-ordered injunction on Halliburton to preserve this material. BP said Halliburton declined the investigation team's requests for equivalent samples of the cement components used on the rig. The investigation team said it was, therefore, unable to conduct any lab testing using Halliburton products.
BP counters the concerns that were raised prior to the explosion by Halliburton over the potential for a severe gas flow problem if a BP plan was used. Halliburton and BP were at odds over a key device, known as a centralizer, that is used as part of the process to plug a deepwater well like the oil giant was doing at the time of the disaster. Halliburton's well design expert testified previously he told BP officials April 15 - five days before the well blew - that fewer centralizers would cause a bigger gas flow problem. Centralizers are meant to ensure casing runs down the center of the well bore. If casing strings are cemented off-center, there is a risk that a channel of drilling fluid or contaminated cement will be left where the casing contacts the oil formation, creating an imperfect seal. BP rejected Halliburton's recommendation to use 21 centralizers. Instead, BP used six. In its report Wednesday, BP said the decision likely did not contribute to the cement's failure to isolate the main hydrocarbon zones or to the failure of the shoe track cement.
In June, the House Committee on Energy and Commerce's chairmen said it was BP that made five crucial decisions before the Deepwater Horizon well blowout that "posed a trade-off between cost and well safety." One of those decisions: BP opted against conducting a "cement bond log" to test the integrity of a cement job at the well. A cement bond log would have cost more than $128,000 and taken 9 to 12 hours to perform, the committee's letter notes.
In May, senior BP drilling engineer Mark Hafle told the Coast Guard and BOEM investigators that BP didn't order the test even though more than 3,000 barrels of mud had been lost while drilling, a possible warning sign.
The committee also criticized BP's well design, questioning its decision to run a single string of steel casing from the seafloor to the bottom of the well. Instead, the committee said, BP could have hung a steel tube called a "liner" from the lower end of the well casing and installed a "tieback" on top of the liner. The latter option would have created a better barrier against the flow of gas, but it would have cost BP up to $10 million more and taken longer, the committee said.