In gas drilling,severe friction and collision may occur between drill collar and well wall due to the lack of the lubrication of drilling fluid. Therefore the drill collar wears rapidly,and may cause failure under complex loads. The worn morphology of drill collar was analyzed and results showed that there are uniform wear,one-side wear and two-side wear. On the basis of data of NC61-90 drill collar failure of Well LJ-1 in northeastern Sichuan and theory of residual strength,residual strength ratio and safety factor,a finite element model was established. The residual strength, residual strength ratio and safety factor were calculated for uniform, one-side and two-side wear respectively. The simulation results showed that the worse of the drill collar wear,the residual strength declines quicker and the strength and safety factor were lower. The reason was that the non-uniform load happened to the worn drill collar while drilling,because of the reduced local thickness of worn drill collar. It is suggested to use low rotate speed of air hammer or the suitable stabilizer in the process of gas drilling,as well as strengthen the management of worn drill collar.%气体钻井中,由于缺少钻井液润滑,钻铤与井壁容易发生剧烈摩擦碰撞,导致钻铤快速磨损,严重时造成钻具失效.首先,分析了钻铤磨损形貌,发现主要有均匀磨损、一侧偏磨和两侧偏磨3种情况.然后,针对气体钻井钻铤磨损较为严重的问题,基于川东北地区L J-1井NC61-90钻铤磨损失效数据和剩余强度、剩余强度率、强度校核、安全系数方法,建立了磨损后钻铤的有限元模型,对钻铤均匀磨损、一侧偏磨和两侧偏磨后的剩余强度、剩余强度率和安全系数进行了计算分析.结果表明:钻铤磨损后剩余强度降低较快,磨损较严重钻铤的强度和安全系数较低,其原因为磨损钻铤壁厚局部变薄,且在钻井过程中承受非均匀载荷.建议气体钻井采用低转速的空气锤钻井工艺,也可适当使用气体钻井专用稳定器,并加强对磨损钻铤的管理.
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