鄂尔多斯盆地延长组地层PDC钻头钻井破岩数值研究

Numerical Study on Rock Breaking of PDC Bit Drilling in Yanchang Formations of Ordos Basin

针对鄂尔多斯地区浅部地层,通过岩心实验获取力学参数,根据岩石力学D-P准则确定地层本构模型,利用剪切损伤原则确定失效标准。在此基础上,建立了PDC钻头动态破岩的非线性三维有限元模型,开展浅层PDC钻头破岩效率研究,进一步分析钻头破岩过程的响应机理与钻进规律。并对泥岩砂岩进行了破岩仿真,考虑了切向力随时间变化规律。计算结果表明,岩石损伤和应力分布能够反映钻头钻进过程中岩石的动态响应;在其他条件相同时,砂岩层段刀齿受力要高于泥岩层段,刀齿侧向力变化幅度大,在往复受力作用下,切削齿易于产生疲劳破坏甚至崩齿现象。以目标区块的砂岩层段为研究目标,其高效破岩的合理转速为5r/s,可在较低的能量消耗下提高钻井效率,为现场施工提供理论指导。

In view of the shallow stratum in Ordos area, the mechanical parameters are obtained by core test,the constitutive model of stratum is determined according to rock mechanics D-P criterion,and the failure criterion is determined by shear damage principle. Based on this,the nonlinear three-dimensional finite element model of PDC bit dynamic rock breaking is established;the rock breaking efficiency of shallow PDC bit is studied;the response machine and drilling law of rock breaking process are further analyzed. The results show that the rock damage and stress distribution can reflect the dynamic response of rock in the drilling process;when other conditions are the same,the force of cutter teeth in sandstone layer is higher than that in mudstone layer,and the lateral force of cutter teeth varies greatly. Under the action of reciprocating force,the cutter teeth are prone to fatigue failure or even collapse. Taking the sandstone interval of the target block as the research object,the reasonable speed of rock breaking with high efficiency is 5 r/s,which can improve drilling efficiency with low energy consumption,and provide theoretical guidance for field operation.