Study on rock-breaking mechanism and bit adaptive characteristics under the action of claw-toe impregnated diamond bit

Abstract

In order to overcome the ingrained belief that the impregnated diamond bit primarily achieves rock-breaking via grinding and micro-cutting and to have a better understanding of the drilling mechanism of the bit, in this work, aiming at the inherent weakness of rock cracks, a claw-toe impregnated diamond bit (CTB) with a self-regenerative structure is innovatively designed. The concept is that the structure of the bit can actively induce the development of cracks inside the rock or create cracks in the dense rock. Through simulation, the differences in hole bottom morphology, drilling efficiency, rotational speed, torque and rock-breaking vibration between conventional bit (CB) and CTB (CTB with two sets of tooth units (CTB-2) and CTB with three sets of tooth units (CTB-3)) are analyzed, and the crack propagation and stress-strain field distribution characteristics of rock are compared when the tooth units of bit (TUBs) press into rock and cause initial damage to rock. Through field tests, the superiority of the claw-toe impregnated diamond bit (CTB) and its rock-breaking mechanism is verified. Compared with the conventional bit (CB), the simulation results show that the claw-toe impregnated diamond bit (CTB) can achieve efficient drilling with smaller rock-breaking torque, more stable rotational speed, and a more apparent shear effect on rock. The mean vibration reaction force of the claw-toe impregnated diamond bit with two sets of tooth units (CTB-2) and claw-toe impregnated diamond bit with three sets of tooth units (CTB-3) increases by 0.78 times and 0.43 times, respectively, and the mean rock-breaking torque decreases by 10.66% and 21.81%, respectively. The structure of the claw-toe impregnated diamond bit (CTB) can force rock to produce more tensile stress concentration areas, induce rock crack initiation, and accelerate rock failure. Field tests show that the service life of the claw-toe impregnated diamond bit with three sets of tooth units (CTB-3) is 1.9 times longer than the mean service life of the conventional bit (CB). Furthermore, the claw-toe impregnated diamond bit (CTB) has obvious structural advantages: it will self-sharpen its structure, maintain its best drilling structure in subsequent drilling, and tear up rock, resulting in better drilling performance.