The Research on Teeth Invade Bottom-Hole Rock Basing on Unified Strength Theory

In order to understand the rock breaking mechanism of cone bit under complex drilling conditions in the deep strata, the problem of teeth intrusion into rock bottom was studied. Under the condition of bottom-hole pressure, the mechanical process of tooth intrusion was analysed based on the unified strength theory. The bottom-hole rock intrusion equation and the cone-rod drilling rate equation with uniform strength parameters were established and the intrusive coefficient without the impact of axial load, invasion depth and bit angle was given. The equation considers the impacts of intermediate stress on intrusive coefficient. The results of the equation and Mohr–Coulomb strength theory are identical when b equals 0. Analyse the impact of angle of internal friction, fluid column pressure, pore pressure and bit angle on intrusive coefficient. The results show that with b, angle of internal friction and bit angle, fluid column pressure and pore pressure increasing, the intrusive coefficient increases, increases exponentially, increases linearly and decreases linearly, respectively.