zon] and double ‘V’ blades—rams with double ‘V’ blades appear to have 15% to 20% lower shear forces than single blade designs. The data received primarily included shear rams having both blades ‘V’ shaped.4 The two data points from shear rams that did not have both blades ‘V’ shaped [as was the case on the Deepwater Horizon] were excluded from statistical consideration” (West Engineering Services 2004, 4-2).

When a signal is sent from the drilling rig to the BOP (on the seafloor) to execute a command, the BOP sends a message back that the signal has been received. However, there are no devices to send a signal that any command has been executed, such as pressure or displacement sensors confirming that hydraulics were actuated or that rams have moved or that pipe has been cut, nor are there any flow sensors measuring whether the well has been sealed.

Additional conclusions can be drawn from the two West Engineering studies. Clearly, the operating success of the BSR was recognized to be much less than 100 percent years before the Macondo well blowout. It appears to be no better than 50 percent, on the basis of the results of the Mini Shear Study described above. This success ratio is inconsistent with the expectations placed on the BOP system as a fail-safe mechanism to close an out-of-control well. If well pressure is assumed to be contained by the annular preventer (assume the maximum rating of the annular preventer to represent this pressure) and if the well pressure differential across the BOP is assumed to be much larger than the hydrostatic pressure exerted by the drilling mud (as was the case in the Macondo well by at least two times), the shear success percentage demonstrated by the first study would decrease even further.

At no time is the drill pipe placed in compression during the tests discussed in the first West Engineering study. In fact, care is taken “to prevent excessive bending of the pipe” (API Specification 16A, Part B4.3.d [1997] (as cited in West Engineering Services 2004, 9-1)). The pipe section below the shear ram is not confined and is free to fall out of the shearing ram during operation. In contrast to this ideal test situation, if the pipe is in compression it may buckle as soon as the ram begins to shear it. The shear ram may not be able to cut the pipe in this condition. If the pipe is cut but cannot move out of the area of the closing rams, the rams may not seal. Sealing was not even considered in the study.

The careful housekeeping necessary to ensure that the correct type of pipe is in the correct position in the BOP stack may be difficult to accomplish in a well control emergency, further decreasing the chance that the shear rams will function correctly. Even with the addition of a CSR, the ability to seal the well is questionable if the pipe either above or below the CSR must be moved out of the way after the CSR cuts the pipe to allow one or more BSRs to seal the well. In a well control emergency there is no assurance, or even a likelihood, that the pipe can be moved at the appropriate moment to allow the BSR to seal. And obvi-


4See Figure 4.1 of West Engineering Services (2004).

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