The rock breaking action of pdc bit is completed by diamond particles. To know the rock breaking effect of the bit, it is necessary to know the rock breaking effect of single diamond. In the hard formation, single diamond under the action of bit pressure makes the rock in a very high stress state (about 4200-5700MPa, some data think it can reach 6300MPa), which makes the rock change from brittle to plastic. The single diamond drills into the formation, and the rock is cut under the action of torque. The cutting depth is basically equal to the drilling depth of diamond particles. This process is like "ploughing", so it is called the ploughing cutting action of diamond bit.
In some brittle rocks (such as sandstone, limestone, etc.), the volume of broken rock is much larger than the ingestion and rotation volume of diamond particles under the simultaneous action of WOB torque. When the pressure is small, small grooves can only be formed along the moving direction of the diamond. Increasing the pressure will break the rocks in the deep and on both sides of the small grooves, exceeding the section size of the diamond particles.
The rock breaking effect of diamond bit is related to lithology and external factors affecting lithology (such as pressure, temperature, formation fluid properties, etc.), and the weight on bit is an important factor. Like the tricone bit, it has three types of rock breaking: surface breaking, fatigue breaking and volume breaking. The ideal rock breaking effect can be achieved only when the diamond particles have enough specific pressure to feed into the formation rock and cause the rock to be broken in volume.
