The report of preliminary findings was released by a committee of the National Academy of Engineering and National Research Council.
"Important decisions made to proceed toward well abandonment despite several indications of potential hazard suggest an insufficient consideration of risks," said Donald Winter, former secretary of the Navy, professor of engineering practice at the University of Michigan, and chair of the study committee.
"It's also important to note that these flawed decisions were not identified or corrected by BP and its service contractors, or by the oversight process employed by the U.S. Minerals Management Service and other regulatory agencies," he added.
However, it cannot be said for sure which mechanisms caused the blowout and explosion, given the deaths of 11 witnesses on board, the loss of the oil rig and important records, and the difficulty in obtaining reliable forensics information from the Macondo well, the report said.
The report cited numerous flawed decisions taken that may have contributed to the disaster:
Continuing abandonment operations at the Macondo site despite several tests that indicated that the cement put in place after the installation of a long-string production casing was not an effective barrier to prevent gases from entering the well.
Accepting the test results as satisfactory without review by adequately trained shore-based engineering or management personnel suggests a lack of discipline and clearly defined responsibilities.
Lack of timely and aggressive action to control the well, and for unknown reasons, hydrocarbons were funnelled through equipment that vented them directly above the rig floor rather than overboard.
Lack of a systems approach to integrate the multiple factors impacting well safety, to monitor the overall margins of safety, and to assess various decisions from a well integrity and safety perspective.
Several questionable decisions also were made about the cementing process prior to the accident, including attempting to cement across multiple hydrocarbon and brine zones in the deepest part of the well in a single operational step, making a hydraulic fracture in a low-pressure zone more likely.
Using a long-string production casing instead of a liner over the uncased section of the well; and deciding that only six centralizers were needed to ensure an even spacing between the formation rock and the casing, even though modeling results suggested that more centralizers would have been necessary.
The type and volume of cement used to prepare for well abandonment and the time provided for the cement to cure may also have impacted the well's integrity.
For its final report, the committee will assess the extent to which there are gaps, redundancies, and uncertainties in responsibilities of multiple agencies and professional societies overseeing deepwater drilling operations, and it will consider the merits of an independent technical review to provide operation checks and balances by enforcing standards and reviewing deviations.
The committee will evaluate possible causes for the failure of the blowout preventer once key data are made available. Data on maintenance, testing, operating procedures, and reliability of alarms and other safety systems on the Deepwater Horizon rig will also be examined; testimony at other hearings indicate that various alarms and safety systems failed to operate as intended. (ANI)