深水钻井隔水管-导管系统波激疲劳分析

波激疲劳是深水钻井隔水管-导管系统最主要的失效模式之一。综合考虑波浪载荷、钻井平台运动和土壤抗力建立了深水钻井隔水管-导管耦合系统波激疲劳分析方法,实例分析了中国南海某井深水钻井隔水管-导管系统波激疲劳寿命,识别出了系统波激疲劳关键部位,并与隔水管常规分析模型的计算结果进行了对比。在此基础上,研究了钻井平台运动幅值、顶张力、下挠性接头转动刚度和井口出泥高度对系统波激疲劳特性的影响。结果表明,常规分析模型将隔水管底部看作固定端导致隔水管波激疲劳损伤过大,而本文提出的隔水管-导管系统分析模型能较好地模拟隔水管实际受力情况;隔水管最大波激疲劳损伤出现在下挠性接头处,导管的最大波激疲劳损伤出现在泥线附近;导管是整个系统中波激疲劳性能最薄弱的环节,适当地减小钻井平台运动幅值、隔水管顶张力、下挠性接头转动刚度和井口出泥高度均能改善导管波激疲劳性能。

Wave induced fatigue analysis on deepwater drilling riser-conductor system

Wave induced fatigue is one of the main failure modes of a deepwater drilling riser-conductor system. In the present paper, a method for calculating wave induced fatigue of the deepwater drilling riser-conductor system was established by comprehensively taking wave load, drilling platform motion and soil resistance into consideration. Wave induced fatigue of the riser-conductor system from a well in the South China Sea was analyzed and key fatigue points of the riser-conductor system were identified, finally the computation result was compared with that calculated by the conventional riser analysis model. On the basis of these results, influences of drilling platform motion amplitude, top tension, rotational stiffness of the lower flex joint and the wellhead mud-line height on the system fatigue were examined. The results showed that the conventional analysis model takes the bottom of a riser as a fixed end, resulting in a too big wave induced fatigue damage of the riser. The riser-conductor analysis model proposed in this paper can simulate the actual load condition of a riser better. The maximum wave induced fatigue damage of a riser lies at the lower flex joint, while that of a conductor occurs around mud-line. The conductor is the weakest point of the wave induced fatigue performance in the whole system. An appropriate decrease in drilling platform motion amplitude, top tension of a riser, rotational stiffness of the lower flex joint and the wellhead mud-line height can all improve the wave induced fatigue performance of a conductor.