Experimental study on drill bit torque influenced by artificial specimen mechanical properties and drilling parameters.

Mechanical properties abruptly change of the coal around small geological structures can easily induce dynamic disasters such as coal and gas outbursts. Some research show that the variation of coal and rock mechanical properties impact the drill bit torque during drilling. However, the influence mechanism is not clear, and the drill bit torque is also affected by the drilling parameters. In this paper, an experimental platform for drill bit torque measurement was set up. Through preparing cement specimens with different mechanical properties, the influence of their mechanical properties and drilling parameters on the drill bit torque were studied. The results show that torque increases with feed force and bit diameter while rotation speed has no significant influence. Feed force exerts the greatest impact and diameter has less effect than the former does. However, if the diameter is too small, discharging drill cuttings will be more difficult, which will result in a sky-high torque. The mechanical properties have a significant influence on drill bit torque, the greater the compressive strength, tensile strength and elastic modulus of the specimens, the smaller the torque, these results are well verified when drilling in composite specimen. This shows that during the drilling process, the variations of the torque-on-bit can reflect mechanical property change of the coal-rock. The results in this paper have a guiding significance for back analysis of mechanical property variations of the coal-rock masses through the drill bit torque, which is beneficial to detect small structures. [ABSTRACT FROM AUTHOR]