Experimental Study on Proppant Backflow and Fiber Sand Control in Vertical Fracture Based on the Visual Diversion Chamber Simulation

Hydraulic fracturing is a critical technical means for enhancing production in gas fields, and post-fracturing flow-back constitutes a crucial phase of fracturing operations. Proppant backflow during the flow-back process significantly impacts both the effectiveness of stimulation and subsequent production. Particularly for tight gas reservoirs, achieving rapid post-fracturing flow-back while preventing proppant re-flux is essential. To date, domestic and international scholars have conducted extensive research on proppant backflow during flow-back operations, with laboratory experimental studies serving as a vital investigative approach. However, due to limitations in experimental apparatuses, further investigation is required regarding the migration mechanisms of proppants during flow-back, proppant backflow prevention techniques, and associated operational parameters. This paper developed a novel visualized flow chamber capable of simulating proppant migration in vertical fractures under closure stress conditions. Extensive proppant backflow experiments conducted using this device revealed that (1) proppant backflow initiates at weak structural zones near the two-phase interface boundaries; (2) proppant backflow occurs in three distinct stages, with varying fluid erosive capacities on proppant particles at each phase; (3) a multi-stage fiber injection sand control process was optimized; (4) at low proppant concentrations (<10 kg/m2), the fiber concentration should be 0.8%; at high proppant concentrations (>10 kg/m2), the fiber concentration should be 1.2%. The recommended fiber length is 6 mm.