Dynamic catastrophe analysis of deepwater mooring platform/riser/wellhead coupled system under ISW

•A dynamic catastrophe model of mooring platform/riser/wellhead system is established.•The model combines mechanical quantitative analysis and process safety analysis.•A method to explore failure risk and process of coupled system under extreme ISW is proposed.•The weakness points include wellhead, mooring system, riser and flex joint.•Two main accident chains of coupled system are identified under different ISW strengths. Mooring platform/riser/wellhead coupled system, as an important and large complex system during offshore drilling operations, is easily affected by internal solitary waves (ISW). The impact load of ISW may lead to failure cascade process and even serious accident consequences to the coupled system. This paper is aimed at proposing a dynamic catastrophic analysis model that combines mechanical quantitative analysis with process safety of mooring platform/riser/wellhead system under ISW. The proposed dynamic catastrophic model can consider limit state of each system used as the failure criterion, including the dragging/fracture of mooring system and the fracture failure of riser/wellhead/conductor system. A dynamic catastrophic analysis method was proposed and a simulation program was also developed based on MATLAB. A case study was presented to reveal the dynamic catastrophic evolution process and the susceptibility of coupled system to ISW. Results indicated that the coupled system would experience wellhead fracture, mooring line dragging or fracture, riser fracture, and flex joint failure under different ISW velocities. Through the quantitative analysis with different ISW strength, two catastrophic scenarios, namely, wellhead fracture-mooring line dragging and mooring line dragging-wellhead fracture-mooring line dragging, occurred.