Abstract:

In the process of windows milling for sidetrack drilling, flexible joint is prone to bending and large deformation. The parameters, such as the weight on bit(WOB), torque and dimensions of flexible joint, are major factors to be considered for ensuring the safety of flexible joint. In order to establish the quantitative relationship between the failure conditions and the influencing factors of flexible joint, the nonlinear mechanical model of the flexible joint considering the dynamic process of windows milling for sidetrack drilling was established in this paper. The stress and deformation distribution were numerically analyzed by ANSYS Workbench, and the influence of WOB, torque, and thickness of the flexible joint on the mechanical behavior were studied. The ultimate WOB and ultimate torque for the three types of flexible joint were calculated. Results demonstrate that the thickness of flexible joint is the primary factor affecting the safety of sidetracking tools, followed by WOB and torque. When the thickness increases by 20mm (from 10.4 mm to 30.4 mm), the maximum compressive stress of flexible joint decreases from 870.64 MPa to 804.04 MPa, the decrease is 7.65 percent. When the WOB increases from 3 t to 13 t, the maximum compressive stress also increases from 838.33 MPa to 860.13 MPa, the increase amplitude is 2.60 percent. When the torque increases from 1.5 kN·m to 10 kN·m, the maximum compressive stress also increases from 842.42 MPa to 849.56 MPa, and the increase amplitude is only 0.85 percent. The mechanical model of flexible joint and failure analysis method proposed in this paper provides a reference for designing operation parameters and tool sizes of sidetrack drilling.

Key words:

 window milling for sidetrack, flexible joint, nonlinear mechanical model, failure analysis

摘要：

挠性短节是套管侧钻开窗钻具组合中易产生弯曲大变形失效的管柱，合理设计钻压、扭矩、挠性短节尺寸等参数，保证挠性短节安全是侧钻成功的基础。为建立挠性短节受力失效条件与影响因素的定量关系，文章考虑开窗钻进的动态过程，建立了挠性短节非线性力学模型，采用ANSYS  Workbench数值分析了挠性短节的应力与变形分布，研究了钻压、扭矩、挠性短节壁厚对挠性短节力学状态的影响规律，得到了三种型号挠性短节失效时的极限钻压和极限扭矩。研究结果表明，挠性短节壁厚是影响开窗钻具安全的首要因素，其次为钻压和扭矩；挠性短节壁厚增加20 mm（10.4 mm增大至30.4 mm）时，开窗钻具最大压应力由870.64 MPa减小到804.04 MPa，减幅为7.65%；钻压由3 t增大到13 t时，挠性短节最大压应力由838.33 MPa增大到860.13 MPa，增幅为2.60%；扭矩由1.5 kN·m增大到10 kN·m，挠性短节最大压应力由842.42 MPa增大到849.56 MPa，增幅仅为0.85%。文章所建立的挠性短节力学模型及失效分析方法为开窗施工参数及钻具尺寸的设计提供了参考。

关键词:

侧钻开窗, 挠性短节, 非线性力学, 失效分析