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V. Conclusions on Well Design, Cementing, and Flow Path

A. Cause of the Failure of the Cement Barrier

Contamination or displacement of the shoe track cement, or nitrogen
breakout or migration, could have caused the shoe track cement barrier to fail.
The Panel found evidence that the most likely reason the shoe track cement
slurry failed is due to contamination in the rat hole portion of the wellbore and
inversion of fluids due to different densities (the mud in the shoe track was
lighter than the unfoamed cement slurry). However, the Panel could not
definitely rule out nitrogen breakout, migration, or over‐displacement in the
shoe track. The Panel concluded that a combination of contamination, over‐
displacement, and/or possibly nitrogen breakout of the shoe cement were
causes of the blowout.

Contamination of the foamed cement in the annulus by the mud, base oil
or cement spacer could have resulted in nitrogen breakout, leading to a failure to
achieve zonal isolation of hydrocarbons in the annulus. The Panel concluded,
based upon its review of forensic evidence that established the absence of free
gas in the annulus, that contamination or nitrogen breakout did not affect
zonal isolation in the annulus.

B. Contributing Causes of the Cement Barrier Failure

Macondo was an exploratory well with limited offset data, and the
differences between calculated and actual pore pressures caused BP to make
revisions to the drilling program and casing setting depths, including the depth
at which BP set the production casing. BP’s internal guidelines stated that
drilling would not be stopped in a hydrocarbon interval, unless doing so was
necessary because of operational/pressure/safety issues. BP’s decision to set the
casing was based on well integrity concerns and a potential safety issue
associated with a zero drilling margin based on 14.1 ppg pressured formation
sand combined with a 12.6 ppg formation pressured zone in the same open‐hole
section taking losses. Additionally, the production casing string shoe was set in
a laminated sand‐shale interface at 18,304 feet measured depth, instead of at a
consolidated shale strata. Placement of the shoe in a laminated sand‐shale zone
increased the likelihood of channeling or cement contamination. The decision to
set the production casing in a laminated sand‐shale zone in the vicinity of a
hydrocarbon interval was a contributing cause of the blowout.

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