280 1. INTRODUCTION With the continuous growth of global energy demand and the ongoing exploration and development of oil and gas resources, drilling engineering is steadily advancing into deeper and more complex formations. Efficient rock-breaking technology is one of the core challenges for improving drilling efficiency and reducing operational costs. Especially in deep formations, complex geological conditions such as high in-situ stress, high hardness, and strong abrasiveness often lead to bottlenecks for traditional single-structure bits (such as pure PDC bits or roller cone bits), including low rate of penetration (ROP), rapid wear, and poor stability(Hu et al., 2021;Zhao et al., 2021). The drill bit is the direct rock-breaking tool and is key to drilling acceleration(Huang et al., 2019;Zhang et al., 2020). Therefore, improving the performance and rock-breaking efficiency of the drill bit—this direct rock-breaking tool—is the most effective direction for solving the problem of low drilling efficiency in hard-to-drill formations. To better address the issues of low ROP and short service life of bits in hard formations and to further enhance the performance of conventional hybrid bits, many scholars have proposed a new hobbing-cone hybrid PDC bit technology that combines the advantages of traditional PDC bits and roller cone bits. For example, Niu et al. proposed a disc-like hybrid bit (DLHB), which achieves an ROP in hard formations that is 30% higher than that of traditional hybrid bits (Niu et al., 2018;Niu et al., 2023), as shown in Figure 1(a). Huang et al. proposed a novel low-torque hybrid bit that can reduce impact vibration on PDC cutters(Huang et al., 2022), see Figure 1(b). Zhang et al. proposed a dual-stage bit, where the internal part breaks rock with rollers and the external part with cutters. This dual-stage hybrid bit exhibits less vibration, smaller lateral forces, and reduced fluctuations in operating parameters(Zhang et al., 2023), see Figure 1(c). The hybrid bit designed by Chen improves efficiency by 15–20% compared to traditional bits in hard rock tunneling(Chen et al., 2023), see Figure 1(d). Figure 1 - Novel PDC bit with spherical-conical hybrid arrangement
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