Simulation and motion analysis of deepwater manifold lifting

The development and utilization of oil and gas resources has expanded to deep water. The installation of a subsea manifold is crucial for developing offshore oil-gas fields. In this study, we used the lifting installation method (LIM) to install a subsea manifold. First, the appropriate environmental parameters were selected through the analysis of environmental loads at the Liwan 3-1 Gasfield in the South China Sea. The wind and wave spectra were selected using noise power density and Joint North Sea Wave Project spectra, respectively. The entire lifting and installation system that responds to environmental loads comprised a vessel, cable, and manifold. The time history of motion response was obtained through simulation and time-domain analysis for the entire lifting and installation process under the combined effect of wind, waves, and current. The motion response of the manifold and the cable tension were analyzed in three stages (entering, steady lowering, and landing phases). The results indicate that the motion responses of the vessel and manifold were highest in the direction of the environmental load. Moreover, the results indicated that the tension of the cable was highest during the entering phase. Furthermore, a heave compensation mechanism was used to reduce the vertical motion of the subsea manifold and the cable tension during the lifting process, which facilitated correct decision-making and reduced the risk of an accident.