Experiments on Abrasive Water Jet Rock Slotting for Improved Perforation Efficiency in Hydraulic Fracturing

Summary Abrasive water jet (AWJ) rock slotting has great potential in hydraulic fracturing. The perforation efficiency of AWJ slotting is higher than that of conventional AWJ perforation. There is an insufficient comprehension of AWJ slotting, including slot evolution, slotting mechanism, and parameter influence. For this study, we conducted experiments of AWJ rock slotting by reciprocating nozzle to investigate the effects of rock type, jet time, jet rate, abrasive volume concentration, jet distance, nozzle reciprocating distance, and nozzle moving rate on slot parameters and the specific energy of rock breaking. AWJ slotting exhibits superior penetration ability and higher perforation efficiency compared with conventional AWJ perforation, as the moving nozzle enlarges the cross-sectional area of the perforation hole, mitigates the jet energy dissipation, and increases the jet action area. The nozzle’s reciprocating movement transforms the slot shape from that of a tip of a brush to that of a goose’s head and finally to a sword. The more reciprocating times of the nozzle, the more symmetrical the slot. The jet rate and jet time mainly affect the slot depth. The jet distance mostly influences the slot thickness. The nozzle reciprocating distance mainly affects the slot length. The jet rate of 200~250 m/s is recommended. The optimal volume concentration of abrasive is 7%. The recommended reciprocating distance of the nozzle is 10 times the nozzle diameter. Increasing the nozzle moving rate to the maximum extent permissible enhances deep penetration and improves energy efficiency. In addition, we designed the bottomhole tool string for AWJ-slotting-assisted hydraulic fracturing. The implementation of AWJ slotting is anticipated to improve the quality and efficiency of multicluster hydraulic fracturing.