Experimental Study of Sand Transport Assisted by Self-Suspended Proppant in Complex Fractures

Self-suspended proppants, which enable clear-water fracturing, represent a promising new class of materials for reservoir stimulation. Given the economic limitations associated with their exclusive use, this study investigates proppant transport behavior in hybrid systems combining self-suspended proppants with conventional 40/70 mesh quartz sand at various mixing ratios. A dedicated experimental apparatus was developed to replicate field-relevant complex fracture networks, consisting of a main fracture and two branching fractures with different deflection angles. Using this system, sand bank formation and proppant distribution were examined for both conventional quartz sand fracturing and fracturing augmented with self-suspended proppants. The effects of slurry discharge volume, proppant mixing ratio, sand ratio, and injection location of the self-suspended proppant on transport and placement behavior were systematically analyzed. According to the results, the incorporation of self-suspended proppants markedly enhances the proppant-carrying capacity of the slurry and substantially modifies sand bank morphology. Increasing the discharge volume raises the inlet slope angle and promotes greater proppant penetration into branch fractures. The proportion of self-suspended proppant governs slurry viscoelasticity and, consequently, proppant settling behavior. As the fraction of self-suspended proppant decreases, the equilibrium height of the sand bank increases, while the proppant mass fraction within branch fractures exhibits a non-monotonic response, initially decreasing and then increasing. Variations in sand ratio alter both overall proppant concentration and the self-suspended proppant-to-water ratio, thereby modulating slurry rheology and influencing proppant placement. In addition, changes in injection location affect near-wellbore vortex structures, leading to distinct sand bank morphologies.