Analyzing the performance of single-cutter cutting rock under bottom-hole pressure conditions

Abstract

Addressing the ambiguity surrounding the process of crack initiation and propagation in rock subjected to confining pressure and hydrostatic pressure, this study integrates laboratory experiments with numerical simulations. First, an analysis is conducted on the cutting force, rock fragmentation energy consumption, rock chip size, and distribution of cutting stress in rocks simultaneously exposed to confining pressure and hydrostatic pressure. Subsequently, an internal crack propagation analysis model for rock is established using the finite discrete element method, and the accuracy of this model is verified through experimentation. The process and characteristics of internal crack propagation during the cutting process are analyzed. Lastly, the variation characteristics of cutting forces under different cutting parameter conditions are compared. The findings indicate that, under identical cutting conditions, confining pressure reduces the degree of granite rock fragmentation, increases the presence of powdery rock debris, and mitigates force fluctuation characteristics, leading to an approximate 17% increase in energy consumption of rock breaking. The presence of confining pressure promotes the generation of micro-cracks within the rock, but restricts the expansion of primary cracks. Notably, shear cracks ahead of the cutting cutter and tensile cracks beneath the cutting path are conspicuously diminished, thereby augmenting the difficulty of rock failure. The elevation of confining pressure and cutting depth emerges as the principal factors contributing to elevated cutting forces, with cutting forces exhibiting exponential growth with increasing confining pressure. At a hydrostatic pressure of 9 MPa, cutting forces escalate by 50 %. Moreover, substantial cutting depth induces discontinuity in the rock failure mechanism. Stress during cutting predominantly concentrates in the vicinity of the PDC cutter front and beneath the cutting trajectory, extending along the advancement direction of the PDC cutter and below the cutting path. These results offer valuable insights for optimizing drilling parameters under confining pressure conditions.