【作者】 李文飞；

【导师】 管志川；

【作者基本信息】 中国石油大学 ， 油气井工程， 2008， 博士

【摘要】 现场资料分析表明,80%的钻柱失效是由于疲劳引起的。采用理论分析的方法,并与现场数据相结合,对直井钻柱的安全可靠性进行了分析研究。钻柱发生屈曲变形,随着钻柱的转动而产生振动,引起钻柱上应力的交替变化,在交变应力作用下,钻柱上的疲劳裂纹不断扩展导致钻柱断裂。根据能量原理推导了钻柱屈曲变形后节距与钻压、转速、扭矩之间的关系模型,为确定钻柱在井眼中的位置,计算钻柱应力提供帮助。在钻柱应力分析的基础上,考虑疲劳因素,建立了钻柱强度的校核模型,与常规方法只基于静载相比,提高了钻柱强度设计的安全性。结合现场数据,分析了钻柱疲劳强度系数随钻井参数的变化规律,得出了随钻压、转速、井深的增加而减小的重要结论,且应用结果也说明了钻柱强度校核必须考虑疲劳的重要性。通过钻柱接头螺纹的受力分析,建立了螺纹牙在轴向载荷和弯曲载荷作用下的变形协调方程,并根据边界条件,推导出了每圈螺纹牙所受载荷的计算公式。结果表明,当钻柱接头受力不变时,随着螺纹牙底倒角半径的增大,螺纹处的应力集中系数是降低的;而强度系数是增大的。基于钻柱疲劳S ? N曲线及修正的Miner线性疲劳累积损伤理论,建立了一种关于钻柱疲劳累积损伤的计算方法,便于钻柱疲劳损伤的度量。算例表明,随着井深的增加,钻柱损伤是减小的;随着转速的增大,钻柱疲劳损伤是增加的,顺序向下倒换钻柱是最佳方法,且倒换6次后钻柱整体损伤趋于平衡。同时,推导出了钻铤疲劳S ? N曲线表达式,能够计算一定可靠度下钻铤的疲劳寿命,便于工程应用。在钻柱受力分析的基础上,提出钻柱上的疲劳裂纹是张开型与撕开型表面复合型裂纹的假设,比较接近实际钻柱,并建立了张开型与撕开型表面复合型裂纹扩展速率的计算模型。分析表明,随着钻压、转速的增加,钻柱的循环次数是减小的。根据钻柱尺寸参数、材料特性参数、钻进参数等数据的分布规律,基于可靠性理论,从概率的角度建立了钻柱可靠度的计算方法,克服了安全系数选取时的经验性,具有一定的先进性。更多还原

【Abstract】 By analyzing the data of drilling string failure, 80 percent of failures are caused by fatigue. Using theoretical analysis method, and combined with data in site, the reliability of drilling string in vertical well was researched.The mechanism of drilling string failure is that vibration of drilling string is generated with rotating because of buckling, so the stress of drilling sting is alternating, under the condition of alternating stress, the crack of drilling sting is propagating. According to the energy principle, the model of relationship between pitch and drilling parameters including of pressure, rotary speed, torque is established, more parameters are considered and closer to the site. Considering fatigue and based on analysis of mechanics of drilling string, strength calculation method is build and increasing safety of drilling string comparing to conventional method that is under the condition of static load. Using data in site, the rule of fatigue strength coefficient with drilling parameters is analyzed, fatigue strength coefficient is decreasing with pressure, rotary speed, depth increasing, and considering fatigue is important. Based on the analysis of mechanics of connection, deformation coordinating equation is established under the condition of axial load and bending load, and according to boundary conditions, the model of load of thread is constructed. The result of analysis of strength calculation shows that when connection stress is constant, stress concentration factor is decreasing and strength coefficient is increasing with the chamfer radius of thread bottom increasing.According to S ? N curve of drilling string and the Miner fatigue accumulative damage theory, calculation method about fatigue accumulative damage of drilling string is build, which can help to weight fatigue damage. The analysis of an example shows that drilling string damage is decreasing with depth increasing and increasing with rotary speed increasing. The method of replacing drilling string with drilling string above it is better, after replacing of six times, damage of all drilling string is same. And S ? N curve of drill collar is derived, which can help to analysis of fatigue life of drill collar.Based on analysis of fatigue crack life, according to character of drilling string mechanics, the assumption that fatigue crack of drilling string is I, III complex crack is suggested, and that is fit for drilling string, and the propagation life of it is researched.According to distribution rule of drilling string size, material character, drilling parameter based on reliability theory, the method of calculating fiduciary level of drilling string is analyzed, which is advanced relativity.更多还原