Rock breaking mechanism of diamond drill bit
The rock breaking effect of the diamond bit is done by diamond particles. To understand the rock breaking effect of the drill bit, it is necessary to understand the rock breaking effect of the single diamond. In the hard formation, the single-grain diamond under the action of drilling pressure puts the rock under extremely high stress state (about 4200-5700 MPa, some data can reach 6300 MPa), which causes the rock to undergo lithological transformation, from brittle to plastic. The single diamond is eaten into the formation and the rock is cut under the action of torque, and the depth of cut is substantially equal to the depth of penetration of the diamond particles. This process is like "plowing the ground" and is called the plow cutting action of the diamond drill bit.
In some brittle rocks (such as sandstone, limestone, etc.), the diamond particles on the drill bit act at the same time as the drilling torque, and the volume of the broken rock is much larger than the intrusion and rotation volume of the diamond particles. When the pressure is not large, only small grooves can be formed along the moving direction of the diamond. Increasing the pressure will break the deep and deep rock of the small groove beyond the cross-sectional size of the diamond particles.
The rock breaking effect of the diamond bit is related to the lithology and external factors affecting the lithology (such as pressure, temperature, formation fluid properties, etc.), and the magnitude of the weight-on-bit is an important factor. Like the roller bit, it has three ways: surface breakage, fatigue fracture and volume breakage. The ideal rock-breaking effect can only be achieved when the diamond particles have sufficient specific pressure to eat into the formation rock and cause the rock to be crushed.