Development of a Cutting Force Model for a Single PDC Cutter Based on the Rock Stress State

Abstract

Polycrystalline diamond compact (PDC) bits are currently the most widely used bits in the petroleum industry. However, the rock-breaking mechanisms of PDC bits are not well understood, especially in deep hard-rock drilling. By modifying the Nishimatsu model, a single PDC cutter force model based on in situ stress is developed in this study. By coupling the mechanical properties of rock and the technological measures of rock breaking, the model can accurately solve the cutting force and assess the rock drillability when applied to a PDC bit. The analysis of research findings shows that the vertical stress initially has a greater impact on the cutting force despite a larger horizontal stress relative to the vertical stress. Moreover, the optimal cutting angle of a PDC cutter is between 15° and 20°. The applicable conditions of the model are obtained experimentally. The model can predict cutting forces in non-expansive rocks well with 2% error. Furthermore, the mechanical-specific energy under low confining pressure has been theoretically demonstrated to increase more quickly than that under high confining pressure. The proposed model can analyse the influence of effective horizontal and vertical stresses and rock strength on the cutting force, which can lead to a better understanding of the rock-breaking mechanisms of PDC drill bits. The results of this work can be used to study PDC bit performance and provide guidelines for the application and design of PDC bits for specific rocks.