Measurement while core drilling based on a small-scale drilling platform: mechanical and energy analysis

How to accurately measure and acquire lithology parameters is the key of drilling exploration in geological engineering. In this present study, a small-scale drilling platform was developed, and a novel sensor that can simultaneously measure axial thrust force, torque and rotation speed was designed, to carry out the test of measuring lithology parameters while drilling (called measurement while drilling, MWD). In this designed platform, multiple sensors were integrated to comprehensively measure the axial thrust force, torque, rotation speed, displacement and oil pressure during the drilling process. Then, MWD tests were performed on the rocks and mortars with different strength grades at rotation speeds of 300 and 400 r/min to investigate the relationship between lithology parameters and drilling parameters. The results indicated that with increasing lithology strength grade, the axial thrust force and the torque increased, while the drilling speed decreased. As the rotation speed increased, the drilling efficiency in terms of mortars increased, and which decreased when drilling into rocks because drill bit wears less in mortars and more in rocks. From the perspective of energy conservation, the value of axial thrust force work, torque work and effective work showed an increasing trend with the growth of strength grade. On this basis, the power function relationships between drilling parameters, effective work and uniaxial compressive strength (UCS) were revealed respectively by using the measured multi-source parameters, that is, the axial thrust force, torque and effective work were positively correlated with UCS, while the drilling speed showed a negative relationship with UCS.