Design and study of special-shaped PDC cutter for hard sandstone strata of Shaximiao Formation

To address the issues of low mechanical drilling speed, severe wear, and high drilling costs of PDC (polycrystalline diamond compact) bits in the hard sandstone strata of the Shaximiao Formation in eastern Sichuan, a comprehensive study was conducted on the rock-breaking performance of special-shaped PDC cutters in the Shaximiao Formation hard sandstone strata. Aiming at the high abrasiveness and hard-plastic characteristics of the sandstone strata in Shaximiao Formation, four types of special-shaped PDC cutters were designed, including axe-shaped cutter, circular-arc curved-surface cutter, axe-shaped curved-surface cutter, and inclined axe-shaped cutter, and a comprehensive rock-breaking specific energy evaluation method combining PDC cutter breaking rock by cutting and pressing was established. Then, using the rock-breaking simulation model, the optimization design for structural parameters of these special-shaped PDC cutters was conducted, and the rock-breaking performance of the optimized PDC cutters was simulated and analyzed. The results showed that the axe-shaped cutter with a blade angle of 130° and the circular-arc curved-surface cutter with a arc radius of 25 mm had the lowest comprehensive rock-breaking specific energy. The final determined arc radius and blade angle of the axe-shaped curved-surface cutter was 25 mm and 130°, and the blade angle and inclination angle of the inclined axe-shaped cutter was 130° and 70°. Four types of special-shaped PDC cutters exhibited significantly lower comprehensive rock-breaking specific energy and blade temperature compared to conventional PDC cutters, with a clear positive correlation between comprehensive rock-breaking specific energy and wear height. The laboratory rock-breaking test results indicated that the axe-shaped cutter and the axe-shaped curved-surface cutter had superior rock-breaking performance. The research results provide a theoretical foundation for the customized design of PDC bits tailored for the hard sandstone strata of the Shaximiao Formation.