Study for Appropriate Determination of Sub-working Layer Width Affecting Drilling Performance of a New Sandwich-type Impregnated Diamond Bit in Drilling of Slipping Formation

This study aims to analyze the impact of the sub-working layer width on the drilling performance of Sandwich-type Impregnated Diamond Bit (SIDB) in extra-hard, compact and weakly abrasive rock formation called the slipping formation and determine the appropriate sub-working layer width for improving the drilling performance. In this study, the rock-cutting simulation using Particle Flow Code in Three Dimension (PFC3D) software based on the discrete element method, the field drilling test and the particle-size analysis of the cuttings produced during the drilling were carried out. The results of the rock-cutting simulation using PFC3D indicate that the distance between two cutters clearly affect the cutting efficiency and the appropriate sub-working layer width for improving the drilling performance is 1.25mm. For the field drilling test, SIDB of Φ59/41 mm with the sub-working layer width of 1.25mm was manufactured and applied to the quartzite formation of Ongjin mining area. The result of field drilling test shows that the rate of penetration (ROP) and the drilling footage are 1.05m/h and 10.8m, respectively, and are 3-5 times bigger than those of the conventional bit. The particle-size of the cuttings produced during the drilling ranges from 34.5-108.6 μm, which is much larger than that of the conventional bit. This indicates that the rock-breaking mode is clearly transferred from micro-cutting mode to the combination mode of micro-cutting and volumetric-breaking. This study has proposed a new design approach to effectively overcome the slipping formation.