Experimental investigation on the sandstone perforation characteristics induced by swirling abrasive water jet

Radial jet drilling (RJD) technology can establish multi-layer, multi-branch networks for high-speed fluid migration within reservoirs. In sandstone geothermal reinjection, they effectively reduce the maximum flow velocity and near-wellbore flow resistance, thereby protecting the reservoir and improving injection performance. The main challenge lies in efficient rock breaking and wellbore formation. This study investigated sandstone perforation characteristics under various abrasive water jet nozzle structures. The tested types included conical straight nozzle (CSN), swirling impeller nozzle (SIN), and straight-swirl hybrid impeller nozzle (SSIN). The effects of jetting pressure, standoff distance, and jetting medium on the perforation diameter, depth, and volume produced by the swirling abrasive water jet (SAWJ) were further analyzed. Results show that all three nozzles produced circular erosion holes: the CSN concentrated jet energy and yielded the smallest diameter but the greatest depth (150 mm); the SIN produced a conical bulge and a “W”-shaped profile with the largest diameter (54.84 mm); and the SSIN formed a “U”-shaped profile with the largest volume (81.84 cm 3 ). Compared with pure water and quartz sand slurry, garnet slurry achieved the greatest perforation depth and volume with lower specific energy and cost. All hole parameters increased with rising jetting pressure. Increasing the standoff distance enlarged the hole diameter, but the depth and volume decreased. Long-duration fixed-point jetting confirmed the feasibility of SAWJ for RJD in sandstone reservoirs. This study provides theoretical guidance for applying SAWJ in radial well drilling within sandstone geothermal reservoirs.