Analysis of VIV-induced fatigue of string-riser coupled system in deepwater
The fatigue damage induced by vortex in a riser occurs frequently during deepwater drilling/completion and testing operations,while the testing string fatigue caused by vortex-induced vibration in a riser also could not be ignored.The stringriser coupled system model was established in the present paper,and the fatigue algorithm was also proposed by considering the characteristics of testing operation in high pressure deepwater gas wells and the interaction between the string and riser.Concentrating on a high pressure deepwater gas well in South China Sea,the vortex-induced vibration mechanism,the fatigue damage rules and the influence factors were investigated.The results show that the multi-modal vibration occurs easier in the string-riser coupled system at a high velocity.The fatigue damage is fluctuating with the increase of the water depth,and the maximum fatigue damage is located on the top side and the lower flexible joint.The fatigue damage of the testing string is about 0.2-0.25 times as big as that of the riser.An appropriate increase of the riser top tension and the string lifting force would effectively improve the vortex-induced vibration fatigue performance of the string-riser coupled system.
deep water drillingtesting stringriservortex-induced vibrationfatigue analysiscontact analysis