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Despite these problems, by April 14, the Deepwater Horizon crew
successfully drilled to the M “56” sand, one of the hydrocarbon‐bearing zones
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that BP geologists and engineers had targeted for the well. Although the
original well plan was to drill approximately 1,800 additional feet, the BP drilling
team in Houston opted to stop drilling the well at a total depth of 18,360 feet
because BP believed the well had reached the base of the target reservoir and that
it had run out of drilling margin. In other words, BP concluded that it could no
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longer safely drill into the formation without creating an underbalanced well (if
the mud was too light) or risking fracturing the formation and threatening well
integrity (if the mud was too heavy). BP planned to run production casing and
temporarily abandon Macondo by sealing it with a surface cement plug so that
another rig could return to the well later and take the steps necessary to complete
the well for production.

On April 19, the Deepwater Horizon crew ran the production casing string
into the well. BP’s engineering team had engaged in significant debate over the
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appropriate design of the casing to run in the final well section. There was
additional debate among BP personnel about the number of centralizers, which
are pieces of equipment used to keep the casing centered in the well, to use on
the final casing string. The crew pumped cement into the annulus and into the
shoe track, the section of the casing between the bottom of the well and the float
valve installed in the well (a large valve designed to allow fluids to flow down
the well while preventing fluids from flowing back up the wellbore during
cementing operations).

The purpose of the cement job was to establish an isolation barrier across
the hydrocarbon zone at the bottom of the well so that hydrocarbons could not

enter the well. In the late hours of April 19and into the morning of April 20, the
rig crew and BP’s cement contractor, Halliburton, pumped cement into the
Macondo well to isolate the hydrocarbon zones. Based on data provided by BP,
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Halliburton designed the cement slurry, which is a mixture of cement, water and

29 BP‐HZN‐MBI‐00126338.
30 Id. As discussed in detail later in this Report, drilling margin is the difference between the
weight of the mud used to drill relative to the pore pressures and the fracture gradient of the
formation. Common industry practice is to use a drilling margin of 0.5 ppg mud weight under
the fracture gradient.
31 IADC Report 4/19/10.
32 Halliburton Post Job Cement Report, BP‐HZN‐CEC011406.

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