Investigation of the breaking manifestations of bedded shale impacted by a high-pressure abrasive water jet

Experiments on high-pressure abrasive water jet (AWJ) crushing shale were conducted with major consideration of bedding planes. The dynamic strain of the shale sample was obtained, and the shale-breaking manifestations and their influencing factors were analyzed by means of both qualitative and quantitative methods. The results indicate that the angle between the jet direction and bedding plane plays a dominant role in the rock-breaking manifestation, with a larger angle leading to a deep perforation hole in the shale and a small angle causing split-shaped breakage. The dynamic strain evolutions combined with the SEM images imply that the shale breaking manifestation of deep perforation holes is caused by the combined actions of huge compressive pressure and the edge chipping effect of abrasives, while the shale breaking manifestation of split-shaped breakage is contributed by huge compressive pressure and the water wedge effect. Additionally, the intermediate jet pressure and abrasive mass flow rate are found to be suitable for the formation of an excellent hole shape. The findings infer that the combination of a large angle, a suitable jet pressure and abrasive mass flow rate is demanded in the application of hydraulic AWJ perforation in shale gas exploitation, while a small angle with large jet pressure is demanded in the application of hydraulic AWJ slotting.