Polycrystalline diamond compact (PDC) bits often encounter challenges such as stick-slip, cutter breakage, and low rate of penetration (ROP) when drilling through complex formations with interlayered soft and hard rocks. Cylindrical PDC cutters have demonstrated promising rock-cutting performance in hard formations, offering a new approach for drilling hard and brittle strata. However, the underlying mechanical mechanisms still need to be thoroughly elucidated. In this study, the rock-breaking mechanism of a single cylindrical PDC cutter is systematically investigated by combining theoretical analysis, finite element (FE) simulation, and laboratory experiments. First, a theoretical model for the cutting force is derived based on Evans' cutting theory, clarifying its mechanical essence. Subsequently, an elastoplastic damage FE model based on the Drucker-Prager criterion is established. This model quantitatively analyzes the effects of the cutter back rake angle (5°-25°) and the rock static elastic modulus (10GPa-50GPa) on the von Mises equivalent stress, equivalent plastic strain (PEEQ), and mechanical specific energy (MSE) during the rock fragmentation process. The results show that the Mises stress increases logarithmically with the increase of the post-cutting angle and the elastic modulus, while the PEEQ strain shows an exponential decreasing trend. The MSE increases with both the back rake angle and elastic modulus; the rock-breaking efficiency is highest at a 5° back rake angle and lowest at 25°. The reliability of the simulation results is confirmed through cross-validation between micro-PDC bit laboratory experiments and numerical simulations. Based on the quantitative results, a small back rake angle of 5° is recommended for hard rocks (elastic modulus > 30GPa) to reduce energy consumption, while a 10°-15° back rake angle is suggested for soft to medium-hard formations to balance efficiency with chip removal. This study provides specific quantitative evidence and practical engineering guidance for the optimal design of PDC bits in heterogeneous formations.

The pore degree prediction method based on well logging interpretation for tight sandstone reservoirs cannot meet the requirements of timeliness and rapidity for well exploration decisions. This paper utilizes the logging parameters during drilling, combined with acoustic time difference experiments, dynamic and static parameter experiments, and full-scale drill bit rock-breaking simulation, to reveal the response characteristics of reservoir properties to the feedback information from logging and rock-breaking and establishes a pore degree prediction method. The results show that as the pore degree decreases, the dynamic and static elastic modulus increases, the rate of penetration decreases, the torque increases, the mechanical specific energy increases, and a mathematical relationship model between pore degree and mechanical specific energy is established, achieving real-time drilling prediction of pore degree. The new method has been applied in the NB block, and the coincidence rate with the well-logging interpretation results reaches over 83%. The research results have provided real-time predictions of reservoir pore degrees and improved the efficiency of exploration decisions.