Study on the Evolution Mechanism of Dynamic Conductivity of Hydraulic Fracturing Fractures Based on Proppant Flowback.

Proppant flowback during the posthydraulic fracturing flowback stage can induce instability of the internal proppant support structure and conductivity degradation within fractures, which are critical factors constraining long-term stable production of low-permeability tight oil and gas reservoirs. However, existing studies have mostly focused on static fracture conductivity evaluation, and the understanding of the coupling mechanism among dynamic proppant migration, particle contact network reconstruction, and time-dependent conductivity evolution during the flow-back process remains insufficient. To address this gap, this study adopts an integrated approach combining visualized physical simulations, confining-pressure conductivity experiments, and numerical simulation. Through a two-dimensional visualized fracture model, the effects of the flowback rate, flowback fluid viscosity, and proppant particle size on particle migration behavior and accumulation morphology evolution were analyzed. Furthermore, combined with confining-pressure core experiments, the synergistic regulation mechanisms of drawdown pressure, fluid viscosity, and proppant size on the flowback rate and fracture conductivity were investigated under in situ stress conditions. The results show that fluid momentum transfer during flowback is the dominant factor inducing proppant destabilization and migration. As the flowback intensity increases, the fluid drag force gradually approaches and exceeds the critical shear resistance provided by the particle contact network, triggering large-scale destabilization and migration of the proppant pack, with the flowback rate increasing significantly. Confinement-pressure experimental results further indicate that conductivity degradation is not caused by a single flowback behavior alone but rather results from a cascade damage process involving proppant migration, particle crushing, stress-induced embedment, and flow channel compaction. Under high drawdown pressure, the internal proppant support structure within the fracture undergoes nonuniform reconstruction, leading to continuous shrinkage of the effective conductive channels, with the dynamic conductivity exhibiting significant time-dependent degradation characteristics. Numerical simulation results further validate the intrinsic relationship between the proppant spatial distribution reconstruction and production decline. This study reveals the dynamic mechanism of fluid-solid coupling, particle destabilization, and conductivity degradation within complex fracture networks during the flowback stage, providing a theoretical basis for optimizing flowback strategies and maintaining the long-term fracture conductivity in low-permeability tight reservoirs.