Probabilistic modeling and evaluation of collision between shuttle tanker and FPSO in tandem offloading

DP shuttle tanker drive-off in tandem offloading poses a threat of collision to Floating Production, Storage, and Offloading unit (FPSO) with potential serious consequences. A two-stage probabilistic model of FPSO and tanker collision in the tandem offloading operation is developed. The first part of analyses based on this model deals with tanker drive-off scenarios. Findings reveal that the tanker drive-off frequency in tandem offloading is high. Based on analyses of incidents, failure prone situations, termed as excessive surging and yawing, under which tanker drive-off frequently happened, are identified. Measures to eliminate excessive surging and yawing, which ultimately reduce tanker drive-off occurrence, are proposed. The second part of analyses deals with recovery action initiated by tanker DP operator in drive-off scenario. Given the favored recovery strategy by the majority of operators, analyses revealed that recovery failure probability is still high due to lack of time for DP operator to initiate the recovery action in tanker drive-off scenario. Measures to increase available time, and to reduce operator reaction time, are proposed to reduce the recovery failure.