In hard formations, the single-grain diamond puts the rock under a very high stress state (about 4200-5700 MPa, some data believes it can reach 6300 MPa) under the effect of weight-on-bit, which changes the lithology of the rock from brittle to plastic. Single-grain diamonds eat into the formation and cut through the rock under the action of torque. The cutting depth is basically equal to the depth of diamond particles. This process is like "plowing the ground", so it is called the plow cutting action of the diamond drill.
In some brittle rocks (such as sandstone, limestone, etc.), the diamond particles on the drill bit at the same time as the weight-on-bit torque, the volume of the broken rock is much larger than the intake and rotation volume of the diamond particles. When the pressure is not large, small grooves can only be formed along the diamond's movement direction. Increasing the pressure will break the rocks in the deep part and the sides of the small groove, exceeding the cross-sectional size of the diamond particles.
The rock breaking effect of diamond drill bits is not only related to lithology and external factors that affect lithology (such as pressure, temperature, formation fluid properties, etc.), but the weight-on-bit is an important influencing factor. It is the same as the cone drill. When rock is broken, there are three ways of surface breaking, fatigue breaking and volume breaking. Only when the diamond particles have sufficient specific pressure to intrude into the formation rock and cause the rock to break up in volume, the ideal rock breaking effect can be obtained.
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