How PDC Bits Conquer Complex Formations?

In the extraction of mineral resources such as coal, oil, and natural gas, as well as in various geotechnical engineering projects, rock-breaking drill bits are widely used as important rock-breaking tools. With the continuous growth in energy demand and the gradual depletion of shallow mineral resources, drilling activities have gradually shifted towards deeper, more complex, and more difficult-to-drill formations. This shift imposes higher requirements on the performance of rock-breaking drill bits.

According to the classification of cutting tooth materials, rock-breaking drill bits are mainly divided into carbide bits and PDC (Polycrystalline Diamond Compact) bits. Carbide bits played an important role in past mining operations, but as the difficulty of extraction increases, their performance gradually fails to meet the demand. In contrast, PDC bits stand out due to their excellent rock-breaking capabilities, with their market size increasing year by year.

PDC Bits and Their Working Principle

PDC bits mainly consist of the bit body, cutting teeth (diamond composite pieces), hydraulic structure, gauge protection surface, and joints. Among these, the cutting teeth, made of diamond composite pieces, are the core of PDC bits. Diamond composite pieces are a new type of composite superhard material synthesized in one go from diamond micro-powder, bonding agents, and carbide substrates under high temperature and ultra-high pressure conditions. They possess extremely high hardness and good toughness.

In the drilling process, the PDC bit, driven by the torque applied by the drilling rig, allows the cutting edges of the cutting teeth to cut into the formation. Due to the high hardness and toughness of the diamond composite pieces, PDC bits can easily penetrate the rock and maintain sharp cutting edges during prolonged rock-breaking operations, working continuously and efficiently.

Based on different manufacturing processes and materials, PDC bits can be divided into matrix type and steel type. Matrix type bits are sintered from tungsten carbide powder, offering high rigidity and hardness, which makes them less prone to damage and provides good gauge protection, though their manufacturing process is relatively complex. Steel type bits are made from medium to low carbon alloy steel through mechanical processing. They ensure processing quality but generally offer lower strength and durability.

PDC Bit Rock-Breaking Mechanisms

The rock-breaking mechanisms of PDC bits mainly include the following:

• Cutting Action: This mainly occurs in softer formations. Under the drilling pressure, the cutting teeth of the PDC bit penetrate the formation, generating a shearing force on the formation as the bit rotates, thereby cutting the formation and forming rock cuttings.

• Fracturing Action: This mainly occurs in brittle rock formations and is characteristic of PDC bits with an arrangement of alternating sharp and rounded teeth. Sharp teeth generate stress fissures in the formation upon contact, while subsequent rounded teeth cut the already stressed formation, thereby improving rock-breaking efficiency.

• Plowing Action: When the rounded teeth of a PDC bit cut the rock, the drilling pressure causes the round cutting teeth to form cracks inside the rock, which expand as the cutting teeth penetrate deeper, ultimately leading to rock fracturing.

• Abrasion Action: This mainly occurs in high-hardness, highly abrasive formations. Due to the high density and difficulty in fracturing of the formation rock, the cutting teeth of the PDC bit repeatedly cut the formation under drilling pressure, grinding it into fine particulate rock cuttings. However, this method accelerates the wear of the cutting teeth.

• Impact Crushing Action: This is mainly evident in PDC composite bits. During drilling, the vibrations generated by the rotation and revolution of the roller bit, as well as the vibrations caused by the uneven bottom hole rock, lead the cutting teeth of the bit to fracture the rock under the dual action of drilling pressure and vibration. This mechanism achieves higher drilling efficiency and longer bit life compared to ordinary PDC bits.