等壁厚螺杆钻具橡胶衬套失效研究

与常规壁厚螺杆钻具相比，等壁厚螺杆钻具以其输出功率大，输出扭矩稳定等优点获得业内认可。随着等壁厚螺杆钻具的逐步推广使用，等壁厚橡胶衬套失效问题也日益突出。橡胶衬套失效以后，螺杆钻具输出性能降低，使用寿命也减小，这对钻井速度和钻井效益都有较大影响。基于热力学原理、Principal strain疲劳算法，建立螺杆马达定转子数值模型，研究了井深、过盈量及粗糙度对橡胶衬套热力学行为的影响，并运用Fe-safe疲劳分析预测橡胶衬套寿命。研究结果表明，等壁厚橡胶衬套主要失效形式为疲劳失效；通过等壁厚与常规壁厚橡胶衬套对比分析可知，等壁厚橡胶衬套较常规壁厚橡胶衬套有更好的密封性能，且对静液柱压力敏感程度更低。对等壁厚橡胶衬套进行设计时，应重点考虑过盈量对橡胶衬套磨损的影响，以确保螺杆钻具安全高效工作。

Study on Rubber Bushing Failure of PDM having Uniform Wall Thickness

With the gradual promotion and application of positive displacement motors (PDM) having uniform wall thickness, the rubber bushing failure has become increasingly prominent. Following the failure of the rubber bushing, the PDM exhibits decreasing output performance and lifespan, which may impact the drilling speed and efficiency substantially. A numerical model consisting of a stator and rotor is established based on thermodynamic principles and the principal strain fatigue algorithm. The impact of well depth, magnitude of interference, and roughness on the thermo-mechanical behavior of a rubber bushing is studied, and the lifespan of the rubber bushing is predicted using Fe-safe fatigue analysis software. According to the research results, the main failure form of uniform-wall-thickness rubber bushings is fatigue failure. Comparison of rubber bushings having conventional and uniform wall thicknesses shows that the uniform wall thickness bushing has better sealing performance and lower sensitivity to static liquid head. While designing a rubber bushing of uniform wall thickness, attention should be paid to the magnitude of interference on the abrasion of the rubber bushing to guarantee the safe and efficient operation of a PDM.