Abstract

The percussive-rotary drilling technique using drill bits with combined cutter types has been widely used for accelerating the drilling of deep wells through hard strata. However, the combination of different cutting cutters and its effect on rock-crushing remain unclear. Thus, there is a lack of reference for selecting proper cutter configurations in actual drilling. To this end, the ABAQUS software was employed to develop a three-dimensional numerical model of the percussive- rotary drilling of the dolomite stratum of the Cambrian Lower Qiulitage Formation with three different cutter combinations: conical cutter & flat cutter, conical cutter & axe-shaped cutter, and flat cutter & axe-shaped cutter. The model was used to investigate the stress distribution and specific energy under axial impact load during the dual-cutter rock-crushing process. The results indicate that the stress waves generated by the different cutting cutters are superimposed on each other; thus, tensile and compressive stresses appear alternately inside the rock along the axial direction in this study. Moreover, the rock-crushing efficiency of the "conical cutter & axe cutter" combination is higher than that of the "conical cutter & flat cutter" combination. Therefore, it is more conducive to the propagation of stress waves inside the rock. Micro-cracks are produced in the rock during the first cutting cycle, reducing the cutting resistance and crushing specific energy when the same position is cut again. This study can provide a theoretical basis for the optimal design on drill bit cutter placement.

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