A semi decoupled analysis model of subsea wellhead based on local equivalent method

Key words:  subsea wellhead  local equivalence  mathematical model  semi-decoupled model

Abstract:

Fatigue caused by wave, VIV and motion of floating drilling platform is one of the main failure modes of the deepwater subsea wellhead, and the method for dynamic analysis of subsea wellhead directly affects the efficiency and accuracy of the subsea wellhead fatigue assessment. Aiming at the problems of time-consuming and low accuracy for dynamic response analysis of the wellhead by using the local fine finite element model, a semi-decoupled analysis model of the subsea wellhead based on the local equivalent method is proposed. The local equivalent method of the wellhead in the global analysis model of the riser-wellhead system is studied, where the equivalent mathematical model of the wellhead consisting of beams and springs is built, and the parameter calculation expressions of beam and spring elements are derived. Then the local equivalent model is used for analysis of the subsea wellhead in the South China Sea. The results of static analysis are compared with those of the local finite element model, and the results of dynamic analysis are compared with those of the full-coupled and uncoupled models. The comparison indicates the correctness and efficiency of the semi decoupled analysis model of the subsea wellhead proposed, thus providing an efficient algorithm for the dynamic response analysis and fatigue assessment of the subsea wellhead system.