Risk Assessment of Riser Operations on DP Drilling Units

Risk of riser operations on dynamic positioning mobile offshore drilling units is addressed in this paper. Primary focus is placed on the blowout risk caused by failure of Emergency Quick Disconnection in the situation of DP failure, i.e. position loss. The risk model is established by an event tree linked with fault trees using RiskSpectrum® software where various equipment failures and operational errors that may lead to failure of DP system and well barriers are identified and modeled. Both overbalanced operation with standard marine drilling risers and underbalanced operations with a set of high-pressure completion/workover risers are analyzed in this paper. And the blowout frequency is presented for a given yearly riser operational activity level. Sensitivity studies are performed for several key variables and recommendations are proposed in order to further reduce the blowout risk of riser operation on DP drilling units.