As previously posted (July 27, 2010), deep water had little to do with the well integrity problems and other contributing factors leading to the Macondo blowout. The Bly (BP) report further confirms this position.
Of the eight key findings in the Bly report (listed below), only number 4 could be considered to be more of a deepwater issue. The BOP failures may also have been influenced by deepwater factors. However, as previously noted, surface BOPs have a much higher failure rate than subsea stacks.
While the Montara blowout was in relatively shallow water, slight variations of findings 1 through 4 were the primary causes of that accident.
BP findings:
- The annulus cement barrier did not isolate the hydrocarbons.
- The shoe track barriers did not isolate the hydrocarbons.
- The negative-pressure test was accepted although well integrity had not been established.
- Influx was not recognized until hydrocarbons were in the riser.
- Well control response actions failed to regain control of the well.
- Diversion to the mud gas separator resulted in gas venting onto the rig.
- The fire and gas system did not prevent hydrocarbon ignition.
- The BOP emergency mode did not seal the well.
Bud's Offshore Energy (BOE) 
The Bly report (page 70) noted some significant “inconsistencies” in the operation of the float shoe/float collar (see below). This is so similar in nature to the “inconsistencies” in the 9 5/8″ cement job on the Montara well to be scary. The bottom line is that both disasters could have been prevented if these “inconsistencies” had been recognised and additional barriers placed above the float collar. In fact even if there are no “inconsistencies”, the placing of an additional barrier or so seems like an exceptionally prudent step, which would not take that much time or effort.
Except from Bly (Page 70)
“Based on information that Weatherford supplied to the investigation team, the float collar conversion should have occurred with a differential pressure between 400 psi to 700 psi. Using the Weatherford flow equation, this would have required a flow rate of 5 bpm to 7 bpm. When the conversion is completed, the two check valves can move into a closed position, which should prevent flow up the casing. When circulation was attempted on this well, either the float collar or the reamer shoe was plugged. The rig crew made nine attempts to establish circulation by increasing pressure on the casing. Circulation was finally established with 3,142 psi. It was not clear to the investigation team whether this pressure converted the float collar, or if it simply cleared a plugged shoe. If the shoe was plugged, the float conversion may not have occurred. Circulation rates throughout the rest of cement placement and displacement did not exceed 4.3 bpm, which was below the specified conversion flow rate.
The second issue concerned another event that may have affected the float collar. This occurred when the Weatherford bottom wiper plug landed on the float collar. This wiper plug separated the cement from the fluids ahead of the wiper plug to prevent cement contamination. When the wiper plug landed on the float collar, pressure was applied to a burst disc in the wiper plug, which allowed circulation to continue. This burst disc was designed to rupture between 900 psi and 1,100 psi. The burst disc did not rupture until 2,900 psi was applied, and cement displacement continued.”