Failure probability analysis for emergency disconnect of deepwater drilling riser using Bayesian network

Drilling risers are the crucial connection of subsea wellhead and floating drilling vessel. Emergency Disconnect (ED) is the most important protective measure to secure the risers and wellhead under extreme conditions. This paper proposes a methodology for failure probability analysis of ED operations using Bayesian network (BN). The risk factors associated with ED operations and the potential consequences of ED failure were investigated. A systematic ED failure and consequence model was established through Fault Tree and Event Sequence Diagram (FT-ESD) analyses and then the FT-ESD model was mapped into BN. Critical root causes of ED failure were inferred by probability updating, and the most probable accident evolution paths as well as the most probable consequence evolution paths of ED failure were figured out. Moreover, the probability adaptation was performed at regular intervals to estimate the probabilities of ED failure, and the occurrence probabilities of consequences caused by ED failure. The practical application of the developed model was demonstrated through a case study. The results showed that the probability variations of ED failure and corresponding consequences depended on the states of critical basic events (BEs). Eventually, some active measures in drilling riser system design, drilling operation, ED test and operation were proposed for mitigating the probability of ED failure.