Transocean Ltd Wednesday said that its own internal investigation into the 2010 Macondo well blowout has found that the disaster, "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 company, which owned the Deepwater Horizon drilling rig that was destroyed in the blowout and subsequent explosion and fire, which killed 11 workers, pointed the blame squarely at Macondo well operator BP.
"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."
Transocean enumerated a series of areas it said led to the April 20, 2010 incident, chief among those that, "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."
Also high on the Transocean list of causes of the disaster was the Macondo well's design and construction, specifically the failure of the well's cement barrier, which allowed Macondo's hydrocarbons to eventually reach 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," Transocean said, citing the "limited margin between the pore pressure and fracture gradients."
DECISION ON CASING DESIGN CITED
But Transocean added that, "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 wellbore."
Among other problems, Transocean's report also cited BP's failure "to properly require or confirm critical cement tests or conduct adequate risk assessments during various operations at Macondo, and the misinterpretation of a "critical negative pressure test."
The Transocean report largely exonerated its workers on the ill-fated drillship. For example, it noted that once an influx of hydrocarbons into the wellbore, and the subsequent "pressure anomaly" was recognized by the crew, they "undertook well-control activities that were consistent with their training including the activation of various components" of the blowout preventer. But the report noted that, by that point, "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."
The report also cited "forensic evidence from independent post-incident testing by Det Norske Veritas (DNV) and evaluation by the Transocean investigation team" that the rig's blowout preventer "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."
