楔形钻齿作用下岩石破碎及微观劣化过程

从理论分析和数值模拟两方面研究楔形钻齿侵入岩石过程中径向裂纹和侧向裂纹的扩展情况。首先根据Marshall的试验研究,分析考虑钻井液压力、侧压作用下岩石在楔形钻齿侵入过程中径向裂纹与侧向裂纹的极限长度公式和最佳齿间距公式,讨论钻井液压力、侧压和齿间距对裂纹扩展的影响;然后利用离散单元方法(PFC2D)研究楔形钻齿侵入过程中岩石的失效以及裂纹扩展情况。研究表明:随着侧压增大,临界侵入深度变大;钻齿下方的损伤区域变小,并且损伤区域变得相对比较平坦,不再凸入岩石内部;钻井液压力增大对径向裂纹的扩展以及损伤区域的扩大有促进作用,径向裂纹长度以及损伤区域随钻井液压力的增大而增大,但损伤区域随着钻井液压力的增大越来越凸入岩石内部;钻井液压力对侧向裂纹的萌生和扩展有抑制作用;合理的齿间距可以产生侧向裂纹重叠区,促进岩石的破碎,提高破岩效率;理论分析结果和数值仿真结果较一致。

Numerical simulation of rock breaking and microscopic deterioration under wedge-shaped drill bit teeth

Theoretical analysis and numerical simulation were conducted in this study to investigate the propagation of radial and lateral cracks during rock breaking using wedge-shaped drilling bit teeth. The formulas for calculating the radial and lateral crack limitation lengths and the optimal space width were derived, in which the effects of hydraulic pressure and lateral pressure were considered based on the experimental research of Marshall, and the effects of hydraulic pressure, lateral pressure and space width on crack propagation were analyzed. A discrete element method (PFC2D) was used to simulate the indentation process of the drilling bit teeth. The results show that, with the indenter penetrating into rock, the sub-vertical cracks can be formed from the damaged zone and it will extend to bottom edge of the rock at last. The initiation and propagation of the sub-vertical cracks are mainly driven by the tensile contact forces. The development of sub-vertical cracks and the damaged rock zone can be restrained with lateral pressure increasing, and the increase of the lateral pressure can lead to an increase in the critical penetration depth, while the size of the damaged zone decreases and its shape flattens. The development of the sub-vertical cracks and the damaged zone can be promoted with the increase of the hydraulic pressure. A reasonable space width of the bit teeth is beneficial to rock fragmentation, which can improve the efficiency of rock breaking.