Study on the Rock-Cutting Mechanism of Shaped PDC Cutters Based on Frequency-Domain Analysis and Probabilistic Analysis of Cutting-Force Fluctuations

Summary With the advance of oil and gas exploration into deep-earth and deepsea domains, drilling operations increasingly face hard, abrasive, and hard-to-drill formations. Under such harsh conditions, conventional cylindrical polycrystalline diamond compact (PDC) cutters have reached their performance limits, prompting the development of shaped cutters with nonplanar geometries. However, the rock-cutting mechanisms of shaped cutters remain insufficiently understood. Most previous studies evaluate performance mainly using mean cutting force and mechanical specific energy, which obscures the stage-dependent and intermittent dynamics of cutter/rock interaction, making it difficult to reveal how geometric features govern force fluctuations and rock fragmentation. To address these limitations, a quantitative and reproducible framework is developed by integrating frequency-domain and probabilistic analyses of cutting-force fluctuations with traditional single-cutter rock-cutting observations. Fast Fourier transform–based band energy decomposition links key frequency bands to rock-breaking stages, while kernel density and tail-index metrics capture intermittency and impact-like high-magnitude events. These interpretations are cross-validated using high-speed imaging of crack evolution and chip formation to reveal geometry-controlled cutter/rock interactions. Four representative shaped cutters were tested on granite. The images captured with a high-speed camera clarified how cutter geometry affects crack initiation and propagation, whereas the frequency-domain and probabilistic analysis quantified the underlying dynamic behaviors of rock-cutting processes. Results show that each cutter type exhibits distinct rock-cutting mechanisms: The cylindrical cutter causes single-cycle block fragmentation; the scribe cutter shortens the contact arc and lowers friction; the axe-shaped cutter produces multistage subfractures; and the triridged cutter generates deeper stress zones with fewer large-cutting-force-magnitude impact events. The strong agreement between spectral-statistical results and visual observations verifies the validity of the proposed approach. By linking force fluctuations to energy consumption and energy distribution across cutting stages, this framework provides actionable guidance for shaped-cutter design and rock-breaking efficiency optimization and offers a practical basis for selecting cutter geometries for hard, abrasive formations in deep and ultradeep drilling.