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ppg reservoir in the same hole‐section had forced our hand. We had
simply run out of drilling margin.

C. Casing Program

Casing programs describe the number and sizes of the casing strings to be
set in the wellbore and are based upon pore pressure and fracture gradient plots.
Casing programs are designed based on a number of factors, including burst and
collapse pressures, tensile strength, drill bit size, anticipated hydrocarbon
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flow, and hydrocarbon type. BP originally designed the Macondo well to
include seven casing strings to reach the target well depth. However, based on
the actual conditions encountered during drilling, BP used nine casing strings to
reach total depth.

Conditions encountered during drilling can drive changes in casing
programs. For example, circulation loss events occurred in the open‐hole section
of the Macondo well. Lost circulation is the loss of drilling fluids (such as
drilling mud and spacer) into the formation. This loss of drilling fluid is
observed during the circulation of drilling fluids. When less fluid is returned up
the well annulus than was pumped into the well through the drill string, this
means a loss of drilling fluid – lost returns – has occurred. These lost returns
were a factor in BP’s decision to limit the well total depth to 18,360 feet (short of
the 20,200 feet originally planned) and also led BP to revise the well’s casing
design program to account for mud weight and fracture gradient drilling margin
issues. Specifically, BP modified its casing program several times because of: (1)
a well control event in March 2010 that resulted in the drill pipe becoming stuck;
(2) changes in pore pressure estimates; and (3) well ballooning. After BP
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revised its casing program, it submitted a revised Application for Permit to Drill
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to MMS for approval.

67 Burst pressure is the theoretical internal pressure differential at which a joint of casing will fail.
Collapse pressure is the pressure at which a tube or vessel will catastrophically deform as a result
of differential pressure between the outside and the inside of the tube or vessel. Schlumberger
Oilfield Glossary.
68 Tensile strength is the force per unit cross‐sectional area required to pull a substance apart.
Schlumberger Oilfield Glossary.
69 Ballooning, in which the formation absorbs drilling mud while the rig’s pumps are activated
and then releases the mud back into the well when the pumps are not active, can be
misinterpreted as a kick.
70 MMS approved: BP’s Application for Permit to Bypass, which added an additional casing
string, on March 15, 2010; BP’s Revised Application for Permit to Bypass, which added a liner, on

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