Rock-breaking efficiency is not so satisfied using the conventional PDC bit, especially in the hard, soft–hard interbedded, and strong abrasive formations in ultra-deep wells. A method is proposed to make full use of stress-releasing effect at bottomhole, thereby improving the rock-breaking efficiency, and a supporting weight-on-bit (WOB) self-adjusting dual-diameter PDC bit (WSDB) has been invented. The WSDB can dynamically adjust the depth-of-cut control characteristics, which could improve the rate of penetration (ROP) while mitigating the stick–slip vibration caused by the rapid change of depth of cut. The stress field of the rock at the bottomhole is calculated with a numerical method, and the working mechanism of the bit is analyzed. The application effect of the WSDB is evaluated through laboratory tests preliminarily. The results show that the stress concentration area on the shoulder of the reaming bit is decreased obviously and a larger stress unloading area emerges in the intersection between reaming and pilot bit. Thus, mechanical specific energy (MSE) can be greatly reduced when the reaming bit drills into this section. Indoor tests show that the maximum ROP of WSDB can be reached up to 70% higher compared to the conventional PDC bit, and higher ROP could be obtained with a relatively lower bit torque. With drilling parameters greater than the critical revolution and WOB, the reduction in MSE can be reached up to 36% during the rock-breaking process. Making further efforts into the optimization of bit structure to reduce the vibration intensity is expected to achieve more improved bit performance.

使用传统的PDC钻头无法达到令人满意的破岩效率，尤其是在超深井中的硬，软-硬夹层和强磨蚀性地层中。提出了一种充分利用井底应力释放效果，提高破岩效率的方法，并发明了一种支重钻压（WOB）自调双径PDC钻头（WSDB）。WSDB可以动态调整切深控制特性，这可以提高穿透率（ROP），同时减轻由于切深快速变化而引起的粘滑现象。利用数值方法计算了井底岩石的应力场，并分析了钻头的工作机理。WSDB的应用效果已通过实验室测试进行了初步评估。结果表明，扩孔钻头肩部的应力集中区域明显减小，扩孔钻头与钻头的交点处出现较大的应力卸载区域。因此，当扩孔钻头钻入该部分时，可以大大降低机械比能（MSE）。室内测试表明，与传统的PDC钻头相比，WSDB的最大ROP最高可以提高70％，并且在相对较低的钻头扭矩下可以获得更高的ROP。如果钻削参数大于临界转速和WOB，则在岩石破碎过程中，MSE的降低可达到36％。期望进一步努力优化钻头结构以减小振动强度，以实现进一步改善的钻头性能。