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On April 19, the day before the blowout, BP pumped cement down the
production casing and up into the wellbore annulus above the uppermost
hydrocarbon reservoir to prevent hydrocarbons from entering the wellbore. As
discussed above, the annulus cement that was placed across the main
hydrocarbon zone was a lower density, nitrified (foam) cement slurry. At the
time of the blowout, the seal assembly had not yet been mechanically locked to
the wellhead housing.

To analyze the probability of this scenario the Panel commissioned
Keystone Engineering Inc. (“Keystone”) to conduct a buoyancy casing analysis.
Keystone analyzed eight production casing static force conditions that could
have acted upon the production casing and wellhead hanger, and possibly
resulted in movement of the casing. Keystone’s analysis found that six of these
eight scenarios were unlikely to have occurred. Keystone presented two
remaining possible scenarios under which seal movement could have resulted
from well pressure and forces. However, the Panel later ruled out both of these
scenarios because well intervention operations following the blowout showed
that the wellhead seal assembly had, in fact, remained intact during the
blowout.
152

When the Macondo well was secured after the blowout, intervention work
began under the direction and supervision of the Unified Area Command with
input from BOEMRE, including the Panel and other federal agencies. This
153
intervention work required the participation of companies involved in the
drilling of the original Macondo well.

During the well intervention operations, observations using remotely
operated vehicles (ROVs) found that the Macondo wellhead seal assembly was
intact. On September 9, 2010, technicians from Dril‐Quip Inc., a contractor
involved in the intervention operations, used a lead impression tool to take an
impression of the hanger and seal assembly. A lead impression tool is a high
tolerance measurement tool that is able to able to detect changes in equipment to
within fractions of an inch. Based on this lead impression, the technicians on the
Development Driller II (DDII) relief well operation concluded that the 9‐7/8 inch

152 Keystone Report, September 2010.
153 The Unified Area Command refers to the unified, interagency response to the Deepwater
Horizon oil spill.

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