Abstract:Under complex conditions， PDC bits are prone to abnormal failures such as cutter breakage， delamination， and fragmentation due to frequent impact vibration. Adopting a backup cutter layout is an effective method to reduce impact loads and improve the load environment. Based on the formation characteristics of the Longmaxi Formation shale in southern Sichuan， a finite element simulation model of the "main cutter-backup cutter" combined cutting was established using Abaqus software and verified by experiments. The effects of backup cutter shape， exposure height difference， and cutting depth on the working load of the main cutter were systematically analyzed. The results show that a reasonable backup cutter layout can effectively share the impact load on the main cutter and reduce stress concentration. The spherical cutter exhibits the best overall stress dispersion effect and the widest applicability， while the truncated cone cutter achieves the highest load-sharing efficiency at an exposure height difference of 0.5 mm and a cutting depth of 1.0 mm. An exposure height difference of 0.5 mm yields the best comprehensive load reduction， but it should be avoided when the cutting depth is 1.0 mm. Without backup cutters， stress concentration is most severe at a cutting depth of 1.0 mm； when matched with appropriate backup cutters， cutting depths of 0.5 and 1.5 mm are recommended. The slope angle of the conical cutter has no absolute superiority or inferiority， requiring coupled matching with the cutting depth and exposure height difference. For drilling in the southern Sichuan shale formation， the spherical cutter is recommended as the backup cutter， with the exposure height difference set to 0.5 mm and the cutting depth controlled at 0.5 or 1.5 mm. The results of this study can provide theoretical support and technical references for the optimized design of customized PDC bits in complex formations.
