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well, and pumped the recovered mud onto the Damon Bankston, a vessel working
alongside the Deepwater Horizon at Macondo. Because of the movement of the
mud, it was difficult for the crew to track fluid volumes in the wellbore and in
the mud pits on the rig.
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Next, crew members turned to conducting negative pressure tests on the
well, which would give the crew information about whether the production
casing cement job was capable of keeping hydrocarbons out of the wellbore. The
crew ran two separate negative tests using different procedures for each test.
Just prior to 8:00 p.m. on April 20, the BP well site leader on duty on the rig,
Donald Vidrine, and Transocean crew members concluded that the second
negative test showed that the final cement job was successful. Vidrine also
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called Mark Hafle, a BP engineer in Houston, around 8:50 p.m. to discuss the
surface plug. During this call, Vidrine described the results of the negative tests.
Hafle questioned Vidrine about the results of the negative test, but he chose not
to investigate further by accessing and reviewing the available real‐time data.
Instead, Hafle chose to rely upon Vidrine’s assurance that the rig crew had
successfully performed a negative test.
42

During the evening of April 20, the Deepwater Horizon crew continued
with the temporary abandonment procedure by opening the BOP and pumping
seawater down the drill pipe to displace mud and a spacer from the riser.
43
During these well activities, the well experienced significant changes in pressure.
Personnel responsible for monitoring the condition of the well, however, did not
recognize these changes as signs of a kick. The crew members shut down the
well around 9:15 p.m. to perform a sheen test on the spacer that they planned to
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send overboard as it was displaced from the well. The decision to send the
displaced spacer overboard rendered Sperry Sun personnel unable to measure
returns on one of the rig’s flow meters. Due to the placement of the flow meters,

40 BP‐HZN‐MBI‐00021238.
41 Testimony of Jimmy Harrell, Joint Investigation Hearing, May 27, 2010, at 90‐91; Testimony of
Miles Ezell, Joint Investigation Hearing, May 28, 2010, at 279‐282.
42 BP‐HZN‐BLY00125470.
43 “Spacer” refers to material that rig crews pump into a well to separate the drilling mud from
seawater. Displacement of mud and spacer are part of the temporary abandonment procedures
discussed in detail in Section IV of the findings and conclusions.
44 Sperry‐Sun rig data, April 20, 2010. The crew performed a sheen test to confirm that all of the
oil‐based mud had been displaced from the riser. A “sheen test” is intended to indicate the
presence of free oil when drilling fluid, drilled cuttings, deck drainage, well treatment fluids,
completion and workover fluids, produced water or sand or excess cement slurry are discharged
into offshore waters.

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