Bud's Offshore Energy (BOE)

Phil Rae piece in Fuel Fix

1. The well clearly had losses through the shoe during the initial displacement of the heavy spacer with seawater, immediately prior to the negative test.
2. Allowing for, and accepting, losses of ~80 bbls during spacer displacement, explains ALL pressure and flow anomalies without the need to create or invoke undocumented and unsubstantiated valve closures or manipulations that contradict witness testimony of events. It also eliminates the need to adopt unrealistically-low pump efficiencies for the rig pumps, hypothetical washed-out tubing and ridiculously high viscosities for the drilling mud, in an effort to fit questionable computer models.
3. Despite extensive examination by investigators and the publication of several reports, the fact that the well experienced losses, making it even more severely underbalanced than was planned, has been given little credence or has received little or no attention, despite several clear indications that this was the case. While this statement regarding losses may be self-evident, its significance on the outcome at Macondo merits closer examination since it explains many previous, apparently-contradictory aspects of the disaster.
4. Under-displacement of heavyweight spacer, as a result of losses during displacement, caused U-tubing and partial evacuation of the kill line, the lower end of which was later refilled with heavyweight spacer, driven by pressure and flow from the formation. The vacuum, initially, and subsequent invasion of heavy fluid rendered the kill line useless for monitoring the well since the line was effectively blind to pressure changes in the well.
5. While initial flow into the well was through the shoe, pressure above the casing hanger seal during the negative test was reduced to levels that could have allowed the casing to lift, compromising the seal and possibly also allowing flow from the external annulus.
6. The well encountered further losses during the second displacement (to displace the riser), after completion of the negative test. These losses, which were perhaps as much as 200 bbls, effectively replaced heavy mud with sea water in the casing below the drill pipe. This further underbalanced the well to the point that it was being kept under control only by pumping friction pressure. As the pump rate was reduced prior to shut down for the sheen test, effectively reducing system backpressure, the now severely underbalanced well began to flow.