钻铤涡动模拟和钻铤接头累积疲劳损伤评估

Whirl Simulation of Drill Collar and Assessment of Cumulative Fatigue Damage on Drill Collar Connection

大多数的钻铤接头失效归因于弯曲振动引起的累积疲劳,其中旋转钻铤偏心引起的涡动是最重要的弯曲振动之一。钻铤和井壁之间的接触引起极度有害的反向涡动,甚至是无序涡动。挪威科技大学的研究人员使用集中质量模型表示钻铤,采用修正Karnopp摩擦模型模拟BHA的黏滑旋转振动。基于涡动时域响应,使用雨流计数法将连续弯曲应力历史分解为若干个应力范围,计算了相关的循环次数,并采用Miner方法评估了累积疲劳损伤。研究结果表明:增大稳定器间隙可能会引起钻铤侧向振动和动力学模拟的不稳定;如果稳定器间隙超过一定值,钻铤会无序侧向间歇撞击井壁;振动是接头疲劳的重要原因,当考虑黏滑振动时,稳定的正向涡动变为无序侧向振动,甚至在较低钻速下,黏滑振动都可能会引起无序侧向振动;在240 h内,无序侧向振动引起钻铤接头累积损伤达1.9%;虽然每小时损伤率仅为0.008%,但如果考虑其他恶劣井下环境,该值可能更大。研究结果有助于缓解钻铤疲劳损伤。

Most drill collar connection failures are attributed to cumulative fatigue caused by bending vibrations,in which the whirl caused by the eccentricity of the rotary drill collar is one of the most important bending vibrations. Contact between the drill collar and the borehole wall causes extremely harmful reverse whirl and even disorder whirl. Researchers from the Norwegian University of Science and Technology used a lumped-mass model to represent the drill collar and simulate the stick-slip rotation of the BHA using a modified Karnopp friction model.Based on the time-domain response of the whirl,the continuous bending stress history is decomposed into several stress ranges using the rainflow counting method. The related cycle times are calculated. The cumulative fatigue damage is evaluated using the Miner method. The results show that increasing the stabilizer clearance may cause instability of lateral vibration and dynamics simulation of the drill collar. If the stabilizer clearance exceeds a certain value,intermittent and disordered lateral direction impacts of drill collar on the borehole wall will be caused. Vibration is an important cause of connection fatigue. When stick-slip vibration is considered,the stable forward whirl will become disordered lateral vibration,even at lower drilling speed. Within 240 h,disorderly lateral vibration could cause cumulative damage of the drill collar to 1. 9%. Although the damage rate per hour is only 0. 008%,but the actual value may be larger if other harsh downhole environments are considered. The study results could help to mitigate the fatigue damage of drill collar.