Failure of a cement barrier in the production casing string was identified as a central cause of the 2010 Gulf of Mexico oil spill, according to the Report Regarding the Cause of the April 20, 2010 Macondo Well Blowout released by the U.S. Department of the Interior, Bureau of Ocean Energy Management, Regulation and Enforcement in September 2011.
According to the report,
The failure of the cement barrier allowed hydrocarbons to flow up the wellbore, through the riser and onto the rig, resulting in the blowout. The precise reasons for the failure of the production casing cement job are not known. The Panel concluded that the failure was likely due to: (1) swapping of cement and drilling mud (referred to as “fluid inversion”) in the shoe track (the section of casing near the bottom of the well); (2) contamination of the shoe track cement; or (3) pumping the cement past the target location in the well, leaving the shoe track with little or no cement (referred to as “over‐displacement”).
Contributing factors to the incident noted in the report included “poor risk management, last-minute changes to plans, failure to observe and respond to critical indicators, inadequate well control response, and insufficient emergency bridge response training.”
Changes to applicable regulations, agency oversight procedures, and the training curriculum for well operators were among the recommendations for future improvement.
