Research on borehole forming characteristics of two-wing polycrystalline diamond compact bit in coal mines

Abstract

ABSTRACT Numerical simulation and field experiments were carried out to study the characteristics of reaming law, bottom-hole topography, and borehole volume in this paper that is a great significance to further understand the rock-breaking mechanism of the drill bit, modification of the calculation model of anchorage length and mechanical specific energy. Firstly, the numerical simulation was employed to analyze the characteristics of boreholes during drilling in different strength rock formations. Secondly, a series of two-wing Polycrystalline Diamond Compact (PDC) bits of different sizes were used for drilling in limestone, sandstone, sandy mudstone, and mudstone that was used to study the bottom-hole topography and reaming law. Finally, the collection of cuttings and recording displacements were carried out when drilling in sandy mudstone that was used to verify the proposed borehole volume calculation model. The results have shown that the reaming range is 0.273 ~ 2.056 mm when the uniaxial compressive strength of rock is between 25 and 98 MPa, and the bottom of the borehole is “bump-like.” The borehole volume calculation model considering the reaming law and the bottom shape of the borehole has improved flexibility. Furthermore, a new model for calculating the anchorage length is obtained in this paper.