The rock-breaking effect of diamond drill bits is accomplished by diamond particles. To understand the rock-breaking effect of drill bits, we must understand the rock-breaking effect of single diamonds. In hard formations, single diamonds put rocks under extremely high stress (about 4200-5700MPa, and some data believe that it can reach 6300MPa) under the action of drilling pressure, causing the rock to undergo a lithology change from brittle to plastic. Single diamonds eat into the formation and cut and break rocks under the action of torque. The cutting depth is basically equal to the penetration depth of the diamond particles. This process is like "ploughing the land", so it is called the plow-like cutting effect of diamond drill bits.
In some brittle rocks (such as sandstone, limestone, etc.), the volume of rock broken by the diamond particles on the drill bit under the simultaneous action of drilling pressure torque is much larger than the volume of diamond particles eaten and rotated. When the pressure is not high, only small grooves can be formed along the direction of diamond movement. Increasing the pressure will cause the rocks in the deep part of the small groove and on both sides to break, exceeding the cross-sectional size of the diamond particles.
The rock breaking effect of diamond drill bits is not only related to the rock properties and external factors that affect the rock properties (such as pressure, temperature, formation fluid properties, etc.), but also the drilling pressure is an important influencing factor. Like roller drill bits, it has three ways of breaking rocks: surface breaking, fatigue breaking, and volume breaking. Only when the diamond particles have enough specific pressure to eat into the formation rock and cause the rock to break in volume, can the ideal rock breaking effect be achieved.
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