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well, the requirement to dispose of the materials onshore could be avoided
because the applicable regulations provide an exemption provided for water‐
206
based drilling fluids and allow such fluids to be disposed overboard.

BP personnel and MI‐SWACO personnel agreed on the use of the lost
207
circulation material “pills” as spacer. On April 20, the rig crew blended the
spacer from the lost circulation materials to a 16.0 ppg density. The rig crew
pumped 454 barrels of spacer into the well, more than twice as much material as
is typically used. The Panel found no evidence that BP considered the possibility
that pumping a large amount of 16.0 ppg lost circulation material into the well
might risk clogging the choke line or the kill line. Nor did the Panel find
evidence that BP discussed this possibility with the rig crew. A clogged choke
line or kill line would lead to pressure differentials with the drill pipe and would
complicate any negative test procedures using either line.

In its post‐blowout investigation, BP concluded that the presence of this
spacer allowed for viscous material to be present across the choke and kill lines
during the negative test and that this possibly plugged the kill line. 208 This is a
possible explanation for the pressure differential between the drill pipe and kill
line.

D. Well Integrity Testing

1. Negative Pressure Test – Planned Procedures

A negative pressure test is critical because it tests the integrity of the
bottom hole cement job, the wellhead assembly, the casing, and all of the seals in
the well. The negative test seeks to create conditions that simulate what will
occur after the well is temporarily abandoned. Heavy drilling mud is displaced
with spacer fluid and seawater. The displacement invites the well to flow as a
way of testing well integrity. The wellbore fluids are replaced such that the
209
wellbore is underbalanced against the formation pressures for the purpose of
testing the barriers that are in place. There are a number of alternative ways a rig

206 See 42 U.S.C. 6921‐6939f (the Resource Conservation and Recovery Act) and 40 CFR §
261.4(b)(5) (exemption for drilling fluids).
207 Lindner testimony at 296‐298.
208 Robinson testimony at 96.
209 Review of Operation Data Preceding Explosion on Deepwater Horizon in MC 252, Dr. John
Smith, 7/1/10 (Smith Report).

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