The numerous technical and operational breakdowns that contributed to the Deepwater Horizon oil rig explosion and spill from the Macondo well in the Gulf of Mexico suggest the lack of a suitable approach for managing the inherent risks, uncertainties and dangers associated with deepwater drilling operations and a failure to learn from previous "near misses," according to an interim report of preliminary findings from a committee of the National Academy of Engineering and National Research Council. The events also suggest insufficient checks and balances for critical decisions impacting the schedule for "abandoning" the exploratory well – or sealing it in transition to production – and for considering well safety.
decisions made to proceed toward well abandonment despite several indications
of potential hazard suggest an insufficient consideration of risks," says
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."
It may not
be possible to definitively establish 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 says. Nevertheless, the committee
believes that it has been able to develop a good understanding of a number of
key factors and decisions that may have contributed to the blowout of the well.
cites numerous decisions that apparently contributed to the accident, beginning
with 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. The decision to accept 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.
In addition, several clear failures in monitoring of the well appear to have
contributed to its blowout; available data show hydrocarbons entered the well
undetected for almost an hour before the first explosion. Timely and aggressive
action to control the well was not taken, and for unknown reasons, hydrocarbons
were funneled through equipment that vented them directly above the rig floor
rather than overboard. These conditions made ignition "most likely,"
the report says. Finally, the blowout preventer did not seal the well once
particular concern is the 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. The
report also notes that a previous loss of hydrocarbon circulation in the
Macondo well more than a month before the accident presented an opportunity to
take actions to mitigate future risks.
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.
final report, due in the summer of 2011, the committee will examine ways to
establish practices and standards to foster a culture of safety and methods to
ensure that schedule and cost decisions do not compromise safety. 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.
Macondo well's blowout preventer was only recently recovered, and is undergoing
forensic analyses. 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 also will be examined; testimony at other
hearings indicate that various alarms and safety systems failed to operate as
Deepwater Horizon Interim Report
November 29, 2010