PDC钻头复合钻进破岩机理及个性化设计探讨

在复合钻进工况下,地面和井下马达的复合驱动虽能使PDC钻头的钻速能得到显著提升,但钻头寿命也会显著缩短。通过研究定向井、水平井下部钻柱的受力变形特性,建立了复合钻进下PDC钻头的运动学模型,研究了转速比、布齿位置、下部钻柱几何状态等对切削齿切削轨迹的影响规律。在此基础上,改进了PDC钻头破岩数字仿真系统,并利用该系统研究了PDC钻头在复合钻进工况下的运动学、切削力学规律以及井底形态特点。研究结果表明:除了高转速因素以外,复合钻进钻头破岩效率增高的主要原因在于PDC钻头切削齿的不平行刮切特性,以及螺杆弯角所导致的钻头牙齿的不均衡切削状态。针对PDC钻头在复合钻井条件下的破岩机理和失效特点,探讨了复合钻进PDC钻头个性化设计的技术思想和实施方法,为复合钻进条件下PDC钻头工作性能的改进提供了理论依据和技术手段。

Discussion on Rock-breaking Mechanism and Individuation Design of PDC Drill Bit in Compound Drilling

The ground and down-hole motor combined drive makes the rate of penetration of PDC drill bit significantly improved, but the bit life will be greatly reduced. By studying the mechanics behavior of drill string at the direction well or horizontal well, a kinematics model of PDC drill bit under compound drilling was established, and the effects of transmission ratio, cutters layout, drill string geometry on cutting trajectory formed by cutters were analyzed. Furthermore, digital drilling simulation technology of PDC drill bit has been developed and enhanced to study on the kinematics, cutting mechanics regularities and characteristics of bottom-hole model in compound drilling of PDC drill bit. It is considered that non-parallel cutting can be formed by PDC cutter, and the imbalanced cutting variation of cutters caused by the pend angle of the screw are the prime reasons for the rate of penetration improved in compound drilling besides high rotation rate. According to rock-breaking mechanism and failure characteristics of PDC drill bit in compound drilling, the technical ideas and implementation methods for individuation design of PDC drill bit in compound drilling have been discussed, which provides theoretical basis and technical methods for the improvement of working for PDC drill bit in compound drilling.