Digital drilling-based determination of rock anisotropy and anisotropic effect on cutter wear

Abstract

Anisotropy affects the mechanical behaviours of rock, especially for application in rock engineering. In this study, a digital drilling method is proposed to evaluate the mechanical anisotropy of rock. In consideration with the critical friction, the cutting efficiency and contact stress are determined from the revised drilling model to characterize the drilling process. For six types of rock, a series of drilling tests are conducted on three axial directions using the coring bit. The anisotropy of rock strength is obtained from the point load test to compare with the anisotropy of drilling characteristics. Correspondingly, an anisotropy criterion is established. A critical point is identified in the evolution of contact stress and the plot of drilling parameters, corresponding to the critical friction. Result indicates that the evolution of contact stress with inclination angle suggests the similar elastic and plastic stages (inclination angles of 5 and 12, respectively). The typical evolution is also confirmed by the critical depth of the friction point. Moreover, the cutting efficiency and contact stress at the critical point show the evident anisotropic characteristic. A comparison of A 1 and A 2 is conducted to determine the anisotropy index of drilling characteristics. Contact stress present the anisotropy sequence as shale (22.45) > gneiss (14.21) > schist 302 (10.74) and blue sandstone (10.07) > granite (7.29) > red sandstone (5.09). The consistency examination with strength anisotropy index suggests that the contact stress has a fitting correlation with an accuracy of 91 %. In summary, the digital drilling-based method provides a reliable evaluation for rock anisotropy, showing potential in practical application.