On the availability of subsea blow-out preventers

This paper describes some analyses that have been undertaken on two samples of field data on submarine BOP failures. One of these databases has been compiled from PETROBRAS Drilling Reports and the other obtained from the SINTEF BOP Database. The usual textbook approaches have been found to be inadequate for the analysis of these data and new methods have been developed and are described. In the past the failure rates for BOP systems have been assumed to be constant, however the analysis presented here provide strong evidence that they are not; and that failure rate of the BOP systems varies during the period of deployment on the wellhead. The implications of this, and the variation in risk during the various phases of well development, upon appropriate target levels of availability and the inspection intervals required to achieve these are discussed.