Experimental study on the flow behaviour of slickwater in hydraulic fractures using PIV

Abstract During hydraulic fracturing of unconventional reservoirs, slickwater entering narrow hydraulic fractures undergoes a complex flow evolution from the near‐wellbore jet region to a fully developed state in the deep fracture; however, its single‐phase flow behaviour within fractures remains insufficiently understood. In this study, a visualized experimental system for flat‐plate fractures was established and combined with particle image velocimetry (PIV) to measure the flow field from the near‐wellbore region to the distal fracture region. By quantitatively characterizing the velocity and vorticity fields, the effects of injection rate, slickwater viscosity, fracture width, and perforation configuration on in‐fracture flow‐field development were systematically investigated. The results show that the flow field can be divided into a high‐speed jet disturbance zone, a turbulent transition zone, and a fully developed flow zone. As the fluid moves away from the perforations, velocity non‐uniformity and vorticity fluctuations continuously decrease, perforation‐induced vortices gradually dissipate, and the flow field ultimately stabilizes. Slickwater suppresses spanwise development and mixing and weakens large‐scale vortex structures, thereby promoting downstream flow stabilization, with higher‐viscosity slickwater exhibiting a more pronounced drag‐reduction effect. Higher injection rates, lower viscosity, smaller fracture widths, and single‐perforation injection all increase the flow‐field stabilization distance. Meanwhile, perforation configuration controls flow development mainly by altering local jet velocity, jet–jet interactions, and jet–wall interactions. These results reveal the spatial evolution of single‐phase slickwater flow in narrow hydraulic fractures and provide an experimental basis for investigating proppant–slickwater two‐phase transport in complex fractures and optimizing hydraulic‐fracturing parameters.