Dynamic mechanisms of plugging and diverting hydraulic fracturing in tight sandstone using fiber-particulate diverters

To address the engineering challenges of simple fracture morphology and limited total fracture area in deep hard rock hydraulic fracturing, a plugging and diverting fracturing technique integrating fibers and multi-sized particles is evaluated. Acoustic emission (AE) monitoring and three-dimensional fracture reconstruction were used to quantify the effects of material composition, injection rate, and particle gradation on fracture evolution. The results indicate that the plugging structure formed by mono-sized fine particles formed unstable bridges, frequently inducing ineffective pressure fluctuations characterized by a “bridging-collapse-rebuilding” cycle, and failed to form an effective flow barrier. The optimized particle gradation (25-, 50-, and 100-mesh at a mass ratio of 6:3:1) increased the secondary pressurization increment to approximately 128 %, promoting large-angle deflection and branch intersection of the primary fracture without chaotic near-wellbore fragmentation. Furthermore, a “high-low-high” variable-rate injection strategy (150–100-150 mL/min) effectively decoupled plug consolidation from fracture propagation, promoting plug densification before secondary fracture extension and thereby enhancing pressure accumulation and fracture network complexity. These findings provide a mechanistic basis for plugging and diverting fracturing in hard rock and support the design of hydraulic preconditioning strategies for deep hard rock excavation.