Hang-off Analysis on Deepwater DST String Evacuation in Typhoon Condition

Abstract A Drill-stem tested (DST) string system requires relatively longer time for full retrieval, and evacuation during typhoon is an important event in deepwater testing. The hang-off DST string system has a high risk as it experiences strong load due to ocean currents and multi-DOF motion of the floating platform. In this paper, a multi-tube model of DST string system that considers multi-point constraints is presented. Hang-off dynamic analysis, platform heading analysis, and evacuation window analysis are conducted. The results show the stress of the DST string system increase dramatically at top. The translational response of the floating platform has a great influence on the safety of the DST string system. The evacuation window is large in the downstream direction and is infeasible in the upstream direction. The operational performance of the DST string system during hang-off evacuation can be improved when driven in a smaller angle with current and orient the platform heading to reduce heave motion.