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Anadarko or MOEX were directly involved in decisions related to the design or
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drilling of the Macondo well.

B. Drilling Margin

Drilling engineers must design a well to manage pore pressure and
fracture gradients at different well depths. Pore pressure is the pressure exerted
by fluids in the pore space of the formation being drilled. Fracture pressure is
the point at which pressure exerted by the drilling fluid in the well would cause
the surrounding formation to fracture. The fracture gradient plot, expressed as a
calculated equivalent mud weight, is a curve that shows the well’s estimated
fracture gradient by depth. During well design, engineers typically use a
graphical representation of the estimated pore pressure, mud weight, and
fracture gradient, which together define the appropriate drilling margins.

Drilling engineers conduct a “leak‐off” test to determine the strength or
fracture pressure of the open formation. This test is usually conducted
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immediately after drilling past the cemented casing shoe in the well. During
the test, the well is shut in and fluid is pumped into the wellbore to gradually
increase the pressure that the formation experiences. At a certain pressure, fluid
pumped into the well will enter the formation, or leak‐off, by moving through
permeable paths in the rock or by creating a space by fracturing the rock. If the
pressure is increased beyond the formation fracture point, fracturing of the
formation can occur. The results of the leak‐off test dictate the maximum
pressure or mud weight that may be applied to the well during drilling
operations before the formation can be expected to take fluid.

BOEMRE regulations require that “[w]hile drilling, you must maintain the
safe drilling margin identified in the approved APD [Application for Permit to
Drill]. When you cannot maintain this safe drilling margin, you must suspend
drilling operations and remedy the situation.” Safe drilling margin can be
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maintained by ensuring that the mud weight remains between the “kick
tolerance” or “kick margin,” which is typically 0.5 pounds per gallon (“ppg”)

58 Data obtained from Halliburton showed that representatives of Anadarko and MOEX
periodically reviewed information related to the Macondo well during drilling.
59 The “casing shoe” is a short steel collar that is typically attached to the bottom of the casing
string. It helps to establish proper positioning of the casing string in the wellbore.
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30 CFR § 250.427(b). BOEMRE regulations do not specify what a “safe drilling margin” is.
There may be instances where a safe drilling margin can be maintained outside the “kick” or
“swab” margins.

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