Improved Calculation Model of Mechanical Specific Energy Based on Single-Cutter Rock-Breaking Mechanism

Summary As oil and gas exploration progresses to ultradeep and 10 000-m depths, insufficient energy supply during rock breaking by downhole polycrystalline diamond compact (PDC) bits presents a critical challenge. Quantifying the energy consumed in PDC cutter/rock interactions is therefore essential for enhancing bit efficiency and minimizing nonproductive energy losses during drilling. Consequently, for this study, we analyzed and calculated the mechanical work and energy consumption associated with cutter/rock interactions in the rock-cutting process of PDC cutter. First, through indoor single-cutter rock-cutting experiments and methods such as high-speed camera real-time observation and 3D morphology analysis of cuttings, the single-cutter rock-cutting mechanism was revealed, and the pivotal role of the rock crushing zone ahead of the cutter in force transmission during single-cutter cutting was clarified. Based on the rock-cutting mechanism, an improved calculation model for rock-cutting mechanical specific energy (MSE) during single-cutter rock cutting was derived, which comprehensively considered the essential force interactions of PDC cutters. Furthermore, starting from the principle of MSE calculation for full-scale drill bits, the same calculation result was derived, achieving mutual validation between the rock-cutting mechanism and mathematical derivation. Finally, the effectiveness of the improved rock-cutting energy calculation model in evaluating the efficiency of single planar cutters and the rate of penetration (ROP) of full-scale drill bits was verified through indoor single-cutter cutting experiments and full-scale bit rock-breaking experiments using two planar cutter profiles. The findings of this work are of significant reference value for the rational application of PDC bits and technological innovation in ROP improvement.