BA6S井钻杆失效机理

Failure mechanism of drillpipe in Well BA6S

针对东海平湖油田BA6S井钻杆严重刺漏问题,通过研究加厚过渡带理化性能、拉弯扭复合作用下过渡带应力分布、内流道流场特征、基于实际井眼轨迹的钻柱动力学特性及钻杆疲劳特征,详细分析了钻杆失效的机理。研究表明:失效钻杆样品涂层的个别部位严重偏薄,管材中含有较高指标的氮化物,易降低钻杆的冲击韧性;复合载荷作用下过渡段具有较高的应力水平,增加了失效风险;钻杆过渡带附近有较为显著的涡动,内部流场对钻杆产生的总压力较大;较大的井眼狗腿度增大了钻柱动态疲劳系数,导致钻柱更易发生疲劳失效。

Aimed at the drillpipe piereement of Well BA6S in Pinghu Oilfield of East China Sea, failure mechanism was researched in detail by analyzing the physical and chemical performances of intermediate belt, the stress distribution and flow characteristics of intermediate belt under the combined action of tension, bending and torsion, and the dynamic characteristics based on actual well trajectory and the fatigue characteristics of drill string. The results show that the individual parts of the coating thickness is seriously thin, more nitrides in the material of drillpipe which reduce impact toughness and high stress on intermediate belt raises the risk of drillpipe failure under combined load. There are distinct whirl phenomenons near the intermediate belt and the total pressure on drillpipe from internal flow field is large. Large dogleg srverity increases the dynamic fatigue coefficient, easily leading to drill string fatigue failure.