Cluster-level proppant transport and placement in propagating multi-cluster fractures: A computational-fluid-dynamics-based wellbore–perforation–fracture coupling method

Multi-cluster hydraulic fractures originate from wellbores and perforations, where stress–shadow interactions significantly alter fracture geometry and slurry hydrodynamics—making cluster-level proppant placement a highly dynamic process. Understanding this transport and placement is essential for effective multi-cluster fracturing, yet its underlying mechanisms remain unclear due to complex fluid–proppant flow within the integrated wellbore–perforation–multi-fracture system. A reliable predictive model is crucial for forecasting production gains and optimizing fracturing design. To address this gap, we developed a CFD-based (computational-fluid-dynamics-based) dimensionless model of perforation-to-fracture transport efficiency via nonlinear regression, which accounts for differences in proppant and fluid allocation. This model is coupled with a 3D multi-planar fracture model based on the displacement discontinuity method and fracture mechanics to quantify slurry and proppant distribution during multi-fracture propagation. Simulation results show bidirectional stress shadows shorten mid-cluster fractures, promoting heel-biased bedload transport and limiting proppant placement in central clusters. Raising injection rate expands propped area and coverage: increasing from 8 to 10 m3·min−1 boosts propped area by 43.1% and coverage by 13.9%, with diminishing returns at 14–16 m3·min−1. Lower proppant concentrations (∼5%) enhance long-range transport and inter-cluster uniformity; 5%–10% raises propped area by 84.2% and coverage by 82.6%, while ∼25% causes interaction-dominated settling and toe-region under-propping. Enlarging proppant size (50–150 μm) intensifies heel accumulation, cutting propped area by 5.2%. Proppant density effects weaken at >14 m3·min−1 due to dominant kinetic energy. This study guides “rate–concentration–size–density” selection to balance cluster effectiveness and long-term conductivity in reservoir stimulation.