Insights of abrasive water jet slotting mechanisms in hard rock using CFD-DEM simulation

Abrasive water jet (AWJ) slotting technology shows great potential for stimulating oil and gas reservoirs, particularly in hard rock formations. Understanding the transport mechanisms of water and abrasives within the slot is crucial for optimizing performance. In this study, a fluid-structure interaction model incorporating slot geometry, water flow, and abrasive particles was developed using a coupled computational fluid dynamics-discrete element method (CFD-DEM). The effects of nozzle position, slot geometry, and jet parameters were systematically examined. Analysis of water turbulence, abrasive velocity distribution, and wall impact forces revealed the fundamental mechanisms of AWJ slotting in hard rock. Slot length determines the slotʼs cross-sectional area and the turbulence intensity, while jet distance and slot depth govern the turbulence pathway. Water turbulence controls jet kinetic energy dissipation, which further affects abrasive acceleration and the resulting impact force on slot walls. Abrasive transport follows a distinct pattern: decelerating during inflow, turning at the slot bottom, and accelerating along the sidewalls toward the annulus via backflow. Notably, impact forces are significantly higher on the slot bottom than on the sidewalls, driven by both abrasive velocity and impact angle. AWJ slotting offers more efficient rock breaking and deeper perforation than conventional AWJ perforation by moving the nozzle to enlarge the slot cross-section, reduce turbulence, and preserve jet kinetic energy for rock removal. A nozzle moving range of approximately 10 times the nozzle diameter is recommended. These findings offer key insights into AWJ slotting in hard rock, highlighting the coupled dynamics of water, abrasives, and slot geometry, and providing guidance for parameter optimization in field applications.