Integrated Monitoring of Lithology Parameters While Drilling in Small-Scale Coring Platform

Understanding the relations between drilling response parameters (drilling speed, axial thrust force and torque, etc.) and rock properties is useful to quickly acquire lithology parameters (rock strength and brittleness, etc.) and dynamically grasp the characteristics of drilling conditions. In this present study, a small-scale core drilling platform was designed to simulate the diamond drilling process in four types of rocks (sandstone, marble, limestone and granite). Moreover, mechanical sensors were developed to dynamically monitor drilling response parameters (axial thrust force, displacement, oil pressure, torque and rotation speed) of drill bits during drilling in rocks. Experimental results indicated that torque and axial thrust force had a positive correlation with rock strength (uniaxial compressive strength (UCS) and tensile strength), while drilling speed was negatively correlated with rock strength. Conversely, the axial thrust force and the torque had a negative correlation with the Brittleness, and the drilling speed was positively correlated with the Brittleness. Based on the investigations on drilling parameters versus time and drilling depth, it could be concluded that, due to the wear and vibration of drill bits, the drilling speed and the axial thrust force decreased, while the torque increased with the increase of rotation speed. The drilling speed with respect to homogeneous lithology was uniform. The average drilling speeds in sandstone, marble and granite at a rotation speed of 300 r/min were 1.9 mm/s, 1.38 mm/s and 0.79 mm/s, respectively. Notably, at a rotation speed of 300 r/min, the relationships between drilling parameters and lithology parameters were established, and the feasibility of this method to understand lithology parameters via drilling parameters was verified. The conclusions obtained can provide an important reference for the dynamic monitoring scheme of rock drilling response parameters in field construction.