Petri-Net Based Contingency Plan Design for Drilling Operations with Mooring Platform/Riser/Wellhead Coupled System Under ISW

Internal solitary waves (ISWs), characterized by their nonlinearity, large amplitude, and destructive potential, pose significant risks during propagation, potentially causing riser fracture and anchor dragging. This paper presents an alternative to the conventional conservative emergency approach of immediate riser disconnection upon ISW detection. The proposed methodology integrates quantitative dynamic model calculations with Petri-net modeling for contingency plan design. The dynamic model of the deepwater drilling riser coupled system facilitates the identification of failure structures and critical failure time points. Through the incorporation of temporal factors into Petri net modeling, the optimal timing for each action step can be precisely determined, preventing resource wastage and structural damage from premature or delayed operations. A case study demonstrates the emergency response process. The analysis yielded five contingency plans during ISW propagation. Dynamic catastrophic analysis indicates prioritization should focus on the lower flex joint angle, followed by platform trajectory and mooring line tension. Certain ISW scenarios necessitate concurrent monitoring of mooring tension adjustment and emergency disconnection. The developed contingency plan effectively reduces operational time and costs while maintaining safety standards.