WELL DESIGN AND CONSTRUCTION
Summary Finding 2.2: The decision to proceed to displacement of the drilling mud by seawater was made despite a failure to demonstrate the integrity of the cement job even after multiple negative pressure tests. This was but one of a series of questionable decisions in the days preceding the blowout that had the effect of reducing the margins of safety and that evidenced a lack of safety-driven decision making.
Summary Finding 2.3: The reservoir formation, encompassing multiple zones of varying pore pressures and fracture gradients, posed significant challenges to isolation using casing and cement. The approach chosen for well completion failed to provide adequate margins of safety and led to multiple potential failure mechanisms.
Finding 2.4: The sequence of fluids used to cement the Macondo well included a low-density foamed slurry followed by a dense un-foamed tail slurry. The foam cement was designed to have a density of 14.5 ppg at the bottom of the well, but at the surface, where the foam was mixed, the density was extremely light at around 6 ppg. The tail slurry had a density of 16.7 ppg. Because of the extreme density imbalance, the heavy tail cement on top of the foamed cement would have been gravitationally unstable near the surface, and it probably fell into and perhaps through the foamed slurry. This would have had the unintended effect of leaving a tail slurry containing foamed cement in the shoe track at the bottom of the casing rather than leaving the heavy, un-foamed tail cement.
Finding 2.5: Foamed cement that may have been inadvertently left in the shoe track would likely not have developed the compressive strength of the un-foamed cement, nor would it have had the strength to resist crushing when the differential pressure across the cement was increased during the negative test.
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