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On the Macondo well, BP had the option to temporarily abandon the well
without setting a production casing, as it had done previously with the Kodiak,
MC 727, Number 2 and Tiber, KC 102, Number 1 wells when faced with similar
narrow drilling margins and lost returns at total depth. BP’s decision to set
casing in the production interval with known drilling margin limits at total
depth was a possible contributing cause of the blowout.

During the production casing cementing operation, rig personnel
continuously monitored the fluids that they pumped into – and that flowed out
of – the well. But rather than measuring flow‐in directly, rig personnel
calculated flow‐in based on the pump’s piston volume output and efficiency.
The crew measured flow‐out based on the Transocean flow meter paddles and
the Sperry‐Sun flow line sonic/radar sensors. The crew also monitored flow‐out
by pit gain volumes. As discussed above, even with properly calibrated flow
measurement devices, there would have been a 10 percent margin of error in the
flow‐out calculations. Dr. Smith, the expert retained by the JIT, used both the
main pit volume data and the calculated cumulative flow‐out versus flow‐in data
to estimate that approximately 2.3 bbls of mud were lost during the production
casing cementing operation. The Panel used actual flow values to calculate that
the losses amounted to approximately 80 bbls (+/‐ 10% based on flow‐in /flow‐
out data). The fact that the Deepwater Horizon crew did not have available to
them accurate and reliable flow‐line sensors during cementing operations in
order to determine whether they were obtaining full returns was a possible
contributing cause of the blowout.

There were a number of limitations in the cementing plan that could have
contributed to the compromise of the cement job, including the following:

 Reducing the bottoms up circulation from 2,760 bbls to approximately 350
bbls could have increased the likelihood of channeling because: a) there
was less cleaning of the wellbore, and b) the reduced bottoms up
prevented rig personnel from examining, prior to cementing, the mud for
potential contamination by hydrocarbons;

 Pumping cement at the relatively low flow rate of 4 bpm could have
decreased the efficiency with which cement displaced the mud from the
annular space, thereby increasing the potential for channeling; and

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