Transocean Issues Findings on Macondo Incident

Thursday, June 23, 2011

Transocean Ltd. has announced the release of an internal investigation report on the causes of the April 20, 2010, Macondo well incident in the Gulf of Mexico.
Following the incident, Transocean commissioned an internal investigation team comprised of experts from relevant technical fields and specialists in accident investigation to gather, review, and analyze the facts and information surrounding the incident to determine its causes.
The report concludes that the Macondo incident was the result of a succession of interrelated well design, construction, and temporary abandonment decisions that compromised the integrity of the well and compounded the likelihood of its failure. The decisions, many made by the operator, BP, in the two weeks leading up to the incident, were driven by BP's knowledge that the geological window for safe drilling was becoming increasingly narrow. Specifically, BP was concerned that downhole pressure -- whether exerted by heavy drilling mud used to maintain well control or by pumping cement to seal the well -- would exceed the fracture gradient and result in fluid losses to the formation, thus costing money and jeopardizing future production of oil.
The Transocean investigation team traced the causes of the Macondo incident to four overarching issues:
--  Risk Management and Communication: Evidence indicates that BP failed
    to properly assess, manage and communicate risk to its contractors.
    For example, it did not properly communicate to the drill crew the
    absence of adequate testing on the cement or the uncertainty
    surrounding critical tests and procedures used to confirm the
    integrity of the barriers intended to inhibit the flow of hydrocarbons
    into the well. It is the view of the investigation team that the
    actions of the drill crew on April 20, 2010, reflected the crew's
    understanding that the well had been properly cemented and
    successfully tested.

--  Well Design and Construction: The precipitating cause of the Macondo
    incident was the failure of the downhole cement to isolate the
    reservoir, which allowed hydrocarbons to enter the wellbore. Without
    the failure of the cement barrier, hydrocarbons would not have entered
    the well or reached the rig. While drilling the Macondo well, BP
    experienced both lost circulation events and kicks and stopped short
    of the well's planned total depth because of an increasingly narrow
    window for safe drilling, specifically a limited margin between the
    pore pressure and fracture gradients. In the context of these delicate
    conditions, cementing a long-string casing would increase the risk of
    exceeding the margin for safe drilling. But rather than adjusting the
    production casing design to avoid this risk, BP adopted a technically
    complex nitrogen foam cement program that allowed it to retain its
    original casing design. The resulting cement program was of minimal
    quantity, left little margin for error, and was not tested adequately
    before or after the cementing operation. Further, the integrity of the
    cement may have been compromised by contamination, instability and an
    inadequate number of devices used to center the casing in the

--  Risk Assessment and Process Safety: Based on the evidence, the
    investigation team determined that BP failed to properly require or
    confirm critical cement tests or conduct adequate risk assessments
    during various operations at Macondo. Halliburton and BP did not
    adequately test the cement slurry program, despite the inherent
    complexity, difficulties and risks associated with the design and
    implementation of the program and some test data showing that the
    cement would not be stable. BP also failed to assess the risk of the
    temporary abandonment procedure used at Macondo, generating at least
    five different temporary abandonment plans for the Macondo well
    between April 12, 2010 and April 20, 2010. After this series of
    last-minute alterations, BP proceeded with a temporary abandonment
    plan that created unnecessary risk and did not have the required
    approval by the MMS. Most significantly, the final plan called for
    underbalancing the well before conducting a negative pressure test to
    verify the integrity of the downhole cement or setting a cement plug
    to act as an additional barrier to flow. It does not appear that BP
    used risk assessment procedures or prepared Management of Change
    documents for these decisions or otherwise addressed these risks and
    the potential adverse effects on personnel and process safety.

--  Operations:

    --  Negative Pressure Test: The results of the critical negative
        pressure test were misinterpreted. Post-incident investigation
        determined that the negative test was inadequately set up because
        of displacement calculation errors, a lack of adequate fluid
        volume monitoring, and a lack of management of change discipline
        when the well monitoring arrangements were switched during the
        test. It is now apparent that the negative pressure test results
        should not have been approved, but no one involved in the negative
        pressure test recognized the errors. BP approved the negative
        pressure test results and decided to move forward with temporary
        abandonment. The well became underbalanced during the final
        displacement, and hydrocarbons began entering the wellbore through
        the faulty cement barrier and a float collar that likely failed to
        convert. None of the individuals monitoring the well, including
        the Transocean drill crew, initially detected the influx.

    --  Well Control: With the benefit of hindsight and a thorough
        analysis of the data available to the investigation team, several
        indications of an influx during final displacement operations can
        be identified. Given the death of the members of the drill crew
        and the loss of the rig and its monitoring systems, it is not
        known which information the drill crew was monitoring or why the
        drill crew did not detect a pressure anomaly until approximately
        9:30 p.m. on April 20, 2010. At 9:30 p.m., the drill crew acted to
        evaluate an anomaly. Upon detecting an influx of hydrocarbon by
        use of the trip tank, the drill crew undertook well-control
        activities that were consistent with their training including the
        activation of various components of the BOP. By the time actions
        were taken, hydrocarbons had risen above the blowout preventer and
        into the riser, resulting in a massive release of gas and other
        fluids that overwhelmed the mud gas separator system and released
        high volumes of gas onto the aft deck of the rig. The resulting
        ignition of this gas cloud was inevitable.

    --  Blowout Preventer (BOP): Forensic evidence from independent
        post-incident testing by Det Norske Veritas (DNV) and evaluation
        by the Transocean investigation team confirm that the Deepwater
        Horizon BOP was properly maintained and operated. However, it was
        overcome by the extreme dynamic flow, the force of which pushed
        the drill pipe upward, washed or eroded the drill pipe and other
        rubber and metal elements, and forced the drill pipe to bow within
        the BOP. This prevented the BOP from completely shearing the drill
        pipe and sealing the well.

    --  Alarms, Muster, and Evacuation: In the explosions and fire, the
        general alarm was activated, and appropriate emergency actions
        were taken by the Deepwater Horizon marine crew. The 115 personnel
        who survived the initial blast mustered and evacuated the rig to
        the offshore supply vessel Damon B. Bankston.

The Transocean internal investigation team began its work in the days immediately following the incident. Through an extensive investigation, the team interviewed witnesses, reviewed available information regarding well design and execution, examined well monitoring data that had been transmitted real-time from the rig to BP, consulted industry and technical experts, and evaluated available physical evidence and third-party testing reports.
The loss of evidence with the rig and the unavailability of certain witnesses limited the investigation and analysis in some areas. The team used its cumulative years of experience but did not speculate in the absence of evidence. The report of the team does not represent the legal position of Transocean, nor does it attempt to assign legal responsibility or fault.
The investigation report and supporting documents are available on the homepage of the Company's website at

Source: Press Release

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