Numerical Simulation of Rock Cracking Using Saddle Polycrystalline Diamond Compact Cutters Considering Confined Pressure and Mechanism of Speed Increase

Abstract

Geothermal energy, recognized as a clean energy source, has attracted widespread attention for its extraction. However, it is located in deep and complex geological formations, presenting a significant challenge to the drilling operations of existing Polycrystalline Diamond Compact (PDC) drill bits. To further understand the rock-breaking mechanism of PDC cutters in deep geological formations and improve rock-breaking efficiency, a finite element model employing the cohesive zone method was developed for a saddle-shaped PDC cutter (SC). This model was validated against experimental simulations, proving its capability to capture real rock crack initiation during the simulation process accurately. By analyzing the formation of cracks under cutting forces, the SC’s rock-breaking mechanism was explored and compared with conventional cutters (CCs), clarifying its advantages. Additionally, the model analyzed the effects of different confined pressures, back rake angles, and structural parameters on crack formation in SC rock-breaking, highlighting directions for structural optimization. Full-scale drill bit rock-breaking simulations were conducted to verify the effectiveness and optimization of single cutter usage. The results indicated that the total number of cracks and the generation of tensile cracks determine the rock-breaking efficiency of the cutter. A lower total number of cracks and a higher proportion of tensile cracks lead to better rock-breaking performances. Due to its unique ridged and curved structure, the SC can generate concentrated and tensile stresses on the rock more effectively, resulting in fewer total cracks and a higher proportion of tensile cracks. The increase in confined pressure suppresses the generation of tensile cracks during rock-breaking, dispersing the rock-breaking energy, increasing the total number of cracks, and reducing rock-breaking efficiency. However, under the same conditions, using SC can effectively address these issues and enhance efficiency. For deep formation drilling, a back rake angle range of 15° to 20° is recommended for SC. The arc radius significantly impacts the SC’s tensile cracks and total number of cracks, with a recommended arc radius range of 50 mm to 60 mm, and the SC structure could be modified from an arc to a straight line and back to an arc. The results contribute to enhancing the efficiency of deep drilling and theoretical research on drill bits.