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Notwithstanding the specific guidance provided by API RP 65, the rig crew filled
the rat hole in the Macondo well with 14.0 ppg synthetic oil based mud (SOBM)
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that was lighter than the cement slurry design. The tail cement was 16.74
ppg. Therefore, the density of the mud the rig crew pumped into the well was
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not adequate to prevent the type of “fluid inversion” (swapping of fluid and
cement) that could compromise the integrity of the cement job.

API RP 65 Section 8.2 addresses well preparation using conditioning
fluids. It states that:

Well preparation, particularly circulating and conditioning fluids in the
wellbore, is essential for successful cementing … Common cementing best
practice is to circulate the hole a minimum volume of one bottoms‐up
once casing is on bottom.

As discussed in detail above, BP only partially circulated the Macondo well prior
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to cementing.

1. Halliburton’s Primary Cementing Best Practices

Consistent with API RP 65, Halliburton’s internal cementing best practices
document also advises that full well circulation be performed prior to cementing,
that lighter weight fluid be used in the rat hole, and that adequate centralization
be installed in the well. Halliburton also recommends that, to improve the
probability of success in the primary cementing job, “[t]he best mud
displacement under optimum rates is achieved when annular tolerances are
approximately 1.5 to 2.0 inches.” As discussed above, the annular tolerance on
the Macondo well was only ¾ inches for the production casing.

Halliburton’s best practices document also addresses gas flow potential.
It states:

Although gas flow may not be apparent at surface, it may occur between
zones, which can damage the cement job and eventually lead to casing

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A rat hole is the extra space drilled beyond the last hydrocarbon zone of interest so that
logging tools (used to evaluate the zone of interest) can be run.
144 BP‐HZN‐CEC0011406.
145 BP‐HZN‐MB1‐00021304.

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