煤层气欠平衡钻井旋转控制头胶芯密封特性分析

旋转控制头胶芯的密封性能是影响煤层气欠平衡钻井施工效果的重要因素。根据煤层气钻井工况，对井口偏心工况、起钻和钻进工况下，旋转控制头胶芯和钻具间的接触压力进行了有限元模拟研究，并分析了胶芯不同结构参数对胶芯密封性能的影响，为煤层气钻井低压密封胶芯的优化设计和研制提供了依据。结果表明:胶芯与钻具间的接触压力随偏心距的增大而增大，且靠近偏心侧的接触压力较大；钻进工况下，钻具本体和接头部分的接触压力都明显小于起钻工况；接触压力随外锥角的减小而增大，随内锥角的减小而减小，但变化量较小；摩擦力随主密封段长度的增加呈线性增加，钻杆接头部分明显大于本体。现场应用实践验证了分析结果的正确性。

Performance analysis of seal rubber on rotary control head in CBM well underbalanced drilling

Sealingperformanceofrubbercoreonrotarycontrolheadistheimportantfactorwhichinfluencestheconstructioneffectof under-balanced drilling for coal bed methane.Based on CBM drilling conditions,the finite element simulation analyses of contact pressures between the rubber core of rotary control head and the drilling tools were conducted under wellhead eccentric condition,trip-out condition and drilling condition,and then the influence of different structural parameters of rubber core on its sealing performance was analyzed,which provides a basis for optimal design and development of low pressure sealing rubber core in coal bed methane drilling.The results show that the contact pressures between the rubber core and drilling tools increase with the growth of eccentricity and the contact pressures neartheeccentricsidearerelativelygreat.Underdrillingcondition,thecontactpressuresofdrillingtoolsandjointswereobviouslylessthan that under trip-out condition.Meanwhile,the contact pressures climb with outer taper angle decreasing and decline with inner taper angle decreasing and the variation is very small.The friction increase linearly with the increase of main sealing section length and the friction of drill pipe joint is apparently bigger than that of drilling tools.the analysis results were proved to be true through field application.