Risk control in the well drilling phase: BOP system reliability assessment

The blowout preventer (BOP) is the main well control device used to ensure the safety of well drilling and intervention operations. The BOP is qualified for the demanding conditions that may come from uncontrolled flow in the well. However, recent accidents and near misses also show that the BOP fails from time to time. The oil and gas industry has been collecting experience data for BOP systems over many decades, and several reports on BOP safety and reliability performance has been published based on this data. The BOP received increased attention after the Macondo well blowout in 2010, and previous BOP safety and reliability performance estimates have been challenged. The objective of this paper is to evaluate some of the recent safety and reliability studies published on BOP systems. Based on the evaluation a new approach for safety and reliability assessment of BOP stack closure elements is presented with a case study for demonstrating its application. The main benefit of the proposed approach is a more efficient explicit trade-off analysis, where the effect of different maintenance strategies are evaluated against typical BOP safety availability targets