Investigation of the rock drilling performance of rotary core drilling

The specific drilling energy and penetration rate are very important performance parameters for drilling. The main objective of this study was to investigate the effect of operational machine parameters and rock properties on drilling performance parameters for rotary core drilling conditions. For this purpose, a rotary core drilling test machine was used to measure drilling performance, taking into account the operational machine parameters (weight on the bit, rotation speed, torque, power of the machine, etc.). The experiments were carried out using 12 different operational conditions, consisting of 3 different rotational speeds (210, 330, and 470 rpm) and 4 different dead loads (50, 70, 90, and 110 kg) on 16 rock samples during the core drilling of rocks with different geological origins, i.e., igneous, sedimentary clastic, and sedimentary carbonated. Subsequently, specific energy values were derived from the experimental values of mechanical and electrical characteristics using relevant empirical models. Among the empirical calculations, the specific energy obtained from the electrical measurements indicates that it is more stable than that of the other empirical approaches. On the other hand, as expected, there is a strong inverse relationship between specific drilling energy and penetration rate. Moreover, regression analysis between the specific energy (470 rpm and 70 kg load) and the properties of the rock samples presents a strong relationship. It is concluded that drilling rate index, Equotip hardness, and applied load are the most influential factors on the drilling performance of rotary drilling. In addition, optimum drilling performance is noted when the penetration rate reaches 1 m/h.