Rock-breaking mechanism of shaped cutters in hard-to-drill formations under in-situ borehole conditions

With ongoing advances in deep oil and gas exploration, the drilling depth of large-borehole sections has steadily increased. Consequently, the geological and engineering conditions encountered during drilling have become increasingly complex, often leading to poor bit performance and high drilling costs. To enhance the rate of penetration (ROP) in hard-to-drill formations, a series of experiments and numerical simulations were carried out under in-situ temperature and pressure conditions. The mechanism of difficult drilling was revealed: under in-situ conditions, large-diameter drill bits are subjected to severe vibration, while rock strength and plasticity increase significantly, thereby restricting cutter penetration into the formation and markedly reducing rock-breaking efficiency. Considering borehole size and in-situ conditions, a discrete element interaction model of rock and shaped cutters was established, with model-experiment deviations within 5.5%. Based on this model, the rock-breaking mechanism of shaped cutters was clarified, and key design parameters of polycrystalline diamond compact (PDC) bits—such as cutter geometry (triangular prismatic cutter), cutter diameter (16 mm), and back rake angle (15°-25°)—were identified. This study provides insights into the rock-breaking process and offers technical support for improving ROP in large-borehole drilling of the challenging formations under in-situ conditions.