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designed to rupture but instead remains intact to prevent mud or spacer from
flowing down the well. If the cement job has gone as planned, the cement should
be in the correct place in the annulus and should fill the shoe track when the top
plug lands.

B. Cement Design and Modeling

BP worked with Halliburton to design the parameters of the Macondo
cement job. Because of the lost returns BP had encountered throughout the
drilling of the Macondo well, BP focused on reducing the chance of additional
losses during the final cement job. BP sought to minimize these losses by
reducing the volume of cement it pumped into the well, lowering the rate at
which cement was pumped into the well and using a nitrified cement slurry for
part of the cement job. As discussed further below, use of lower density nitrified
foam cement offered advantages in terms of reducing the risk of formation
breakdown, but also presented technical challenges in ensuring that the cement
mixture is stable.
89

1. Cement Volume

BP chose to limit the height of the cement in the annulus because the
higher the annular cement column, the more pressure the cement would exert on
the formation below, increasing the likelihood of additional lost returns and
potential for fracturing. BP engineers proposed to set the top of the cement in
the annulus at about 17,300 feet total depth, which was approximately 500 feet
above the uppermost hydrocarbon zone. MMS regulations required the
90
cemented annular space in a production casing job to be 500 feet above the
uppermost hydrocarbon zone.
91

89 On August 1, 2011, Oilfield Testing and Consulting (“OTC”) completed a forensic analysis of
the cement samples mixed to replicate the cement slurries that were pumped into the Macondo
well. OTC’s analysis revealed a range of potential cement setting times for the foamed and
unfoamed cement. Several of the samples tested revealed setting times greater than 18 hours (the
time period between the completion of the cement job and the start of the negative tests). See
OTC Report at page 30. The Panel, however, found that there was strong evidence that the
cement had set prior to the time the rig crew performed the negative test. See
http://www.oilspillcommission.gov/sites/default/files/documents/Chevron%20letter%2010%2026
%2010.pdf.
90 BP‐HZN‐MBI0023746. “Top of cement” is the depth in the well where the cement that has
already been set in the well ends.
91 30 CFR § 250.421.

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