Particle-laden flow diversion at a fracture junction: Mechanisms and controls

Proppant diversion in branched fractures is a confined particle-laden flow process that governs effective support in complex fracture networks; however, the particle-scale mechanisms controlling diversion across branch geometries remain insufficiently understood. In this study, coupled computational fluid dynamics–discrete element method simulations were performed to investigate proppant diversion from a primary fracture (PF) into vertical and horizontal secondary fractures (SFs). The diversion process was quantified using sand-dune geometry, particle trajectories, velocity responses, and statistical comparisons between captured and bypassed particles. The results reveal a junction-scale capture–bypass mechanism in which diversion is controlled by the competition between branch-directed drag induced by flow deflection and the streamwise inertial persistence of particles approaching the junction. In the vertical SF, diversion evolves from a drag–gravity-coupled regime to a shear-enhanced, drag-dominated regime. By contrast, diversion into the horizontal SF is mainly drag-driven; gravity promotes particle settling in the PF but contributes little to lateral entry. Within the investigated ranges, the proppant diversion ratio increases with injection velocity, decreases with proppant concentration and proppant size, and varies non-monotonically with fluid viscosity. Parametric response identifies injection velocity and proppant concentration as the primary controls on diversion, whereas fluid viscosity and proppant size play secondary roles. These findings clarify the mechanisms governing capture and bypass in confined particle-laden branching flows and provide a physical basis for interpreting proppant partitioning in complex fracture networks.