基于HJC模型的旋冲钻井PDC钻头破岩机理研究

Study on Rock-Breaking Mechanism of PDC Bits in Rotary Percussive ‌Drilling Based on HJC Model

  • 摘要: 旋冲钻井技术是一种针对深层硬岩的高效破岩方法,但现场应用过程中存在提速效果不稳定、冲击参数与地层匹配性差等问题。针对该问题,利用四川盆地须二段、栖霞组、茅口组和龙马溪组的岩样进行了抗拉试验、单轴及三轴压缩试验、Hopkinson压杆冲击试验,确定了HJC (Holmquist−Johnson−Cook)本构模型参数,通过PDC单齿落锤冲击试验验证了模型参数的正确性。基于四川盆地地层的本构模型参数,建立了全尺寸钻头旋冲钻进数值模拟模型,分析了旋冲钻井破岩过程中轴向冲击参数和岩石力学参数对旋冲钻进效果的影响规律。研究结果表明:建立的模型能够模拟旋冲钻井过程,当其他参数均相同时,轴向冲击波为矩形波时的钻进速度和效率最高,为锯齿波和正弦波时的破岩效果次之;旋冲钻进的速度和效率受轴向冲击频率和冲击幅度的影响较大,冲击频率存在最优值,在一定程度上提高冲击幅度有利于提高钻进速度和效率;四川盆地须二段等4个关键层位岩石的最优冲击频率为10~18 Hz,其与岩石的脆性指数呈线性负相关。四川盆地关键层位HJC模型参数确定方法及结果可为后续研究提供参考,模型数值分析结果可为四川盆地旋冲钻井工具参数的选取提供理论依据。

     

    Abstract: Rotary percussive drilling technology is an efficient rock-breaking method for deep hard rocks, but it has problems in on-site application, such as unstable acceleration effect and poor matching between impact parameters and formation. In response to this issue, tensile tests, uniaxial and triaxial compression tests, and Hopkinson bar impact tests were conducted on rocks from the second member of Xujiahe Formation, as well as Qixia, Maokou, and Longmaxi formations in the Sichuan Basin. The parameters of the (Holmquist−Johnson−Cook) (HJC) constitutive model were determined, and the correctness of the model parameters was verified by establishing a PDC single-cutter drop hammer impact test. Based on the parameters of the geological constitutive model in the Sichuan Basin, a numerical simulation model for rotary percussive drilling of full-size drill bits was established. The influence of axial impact parameters and rock mechanical parameters on the drilling effect of rotary percussive drilling during rock-breaking was analyzed. The results show that the established model can reproduce the rotary percussive drilling process. When all other parameters are the same, the drilling speed and efficiency of rectangular impact loads are the highest, followed by the rock-breaking effect of serrated and sinusoidal loads. The speed and efficiency of rotary percussive drilling are greatly affected by the impact frequency and amplitude, and there is an optimal value for the impact frequency. To some extent, increasing the impact amplitude is beneficial for improving the drilling speed and efficiency. The optimal impact frequency for rocks in the second member of Xujiahe Formation and other key horizons of the Sichuan Basin is 10–18 Hz, which is linearly negatively correlated with the brittleness index of the rock. The determination method and results of the key horizons’ HJC model parameters in the Sichuan Basin can provide reference for subsequent research. The numerical analysis results of the model can provide theoretical support for recommending the parameters of the rotary percussive drilling tool in the Sichuan Basin.

     

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