This paper presents an experimental study of waterjet drilling on the Longmaxi Shale rock to understand the fragmentation behaviors and their mechanics. The homogenous sandstone was the candidate of the control group. The macro fragmentation behaviors and their micro structures were acquired by the Scanning Electron Microscope (SEM) and Computed Tomography (CT) techniques. Results show that there are big difference of fragmentation behaviors between shale and sandstone. The efficiency of shale waterjet drilling is ultralow, which the erosion rate and the ultimate drilling depth cannot reach the half of those of sandstone. For the initial crushing hole, the compression-shear failure does not happen since the static pressure of waterjet is lower than the compression strength. However, the tensile fracture occurs and makes the rock spallation. In the state of the deep hole producing, the waterjet impinging force is not able to make the rock tensile or shear failure. Only the mineral particle erosion appears due to the high velocity erosion. This work provides the theoretical guide for improving the shale rock drilling efficiency by water jetting.

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