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- 2017
硬地层复合钻头破岩特性与提速机理研究
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Abstract:
PDC-牙轮复合钻头是一种综合了PDC钻头与牙轮钻头结构特点和工作原理的新型钻头，能更高效地钻进硬地层。但由于对其破岩机理认识不足，使得PDC-牙轮复合钻头的研发具有盲目性，推广受限。基于弹塑性力学和岩石破碎学，采用Drucker-Prager准则描述岩石本构关系，塑形应变作为破岩判据，通过有限元法建立全尺寸复合钻头和PDC钻头动态破岩的非线性动力学模型，分析了复合钻头作用下硬地层岩石的破坏机制，对比了硬地层中两种钻头的动态破岩过程。结果表明：复合钻头钻井能满足井壁稳定性的要求，然而一旦井壁失稳，井壁岩石将大块脱落；以拉应力破岩为主是复合钻头在硬地层中大幅提高机械钻速的原因之一；硬地层中复合钻头扭转振动低于PDC钻头，破岩效率更高；由于牙轮滚动的多边形效应，复合钻头沿钻进方向对岩石的冲击较PDC钻头更大，能更快钻进硬地层。
A hybrid drill bit combines the structural features and working principles of PDC drill bit and cone drill bit, being able to drill hard formation more efficiently. But its research and development is blind and its promotion is limited due to lack of knowledge about its rock breaking mechanisms. Based on elastoplastic mechanics and rock breaking theory, 3D non-linear dynamic simulation models of dynamic rock breaking with full-gauge hybrid drill bit and PDC bit are established with the finite element method. The constitutive relation of rock is described by Drucker-Prager criteria and the plastic strain is used as the criterion for describing the rock breaking. The failure mechanisms for rock breaking in hard formation with the hybrid drill bit are studied. The dynamic rock breaking with hybrid drill bit in hard formation are compared with that of PDC drill bit. The comparison results show that the well drilled by hybrid drill bit can satisfy the borehole wall stability requirements but that the sidewall rock may fall off. This partly explains the reasons why the use of hybrid drill bit significantly enhances the penetration rate in hard formation and why the rock is broken mainly by tensile stress. The torsional vibration of hybrid drill bit is lower than that of PDC drill bit and the rock breaking efficiency is higher in hard formation. The impact of hybrid drill bit on rock is greater than that of PDC drill bit due to the polygon effect of cone drill bit during scrolling; therefore the hybrid drill bit can drill rock faster than PDC drill bit in hard formation
