Numerical simulation of fiber–proppant cluster settling based on a coarse-grained DEM-CFD method

Hydraulic fracturing is a key technology for the efficient development of unconventional resources such as shale oil and gas, and the effective preservation of fracture conductivity is a core factor determining stimulation performance. Fiber-laden proppants can form cluster structures within fractures, thereby constructing stable “tube-bundle-like” conductive channels and significantly enhancing fracture conductivity. To address the challenges associated with fiber–proppant settling, including strong solid–liquid two-phase coupling, complex particle morphologies, and the excessive computational cost of full-scale simulations, this study introduces a coarse-grained modeling method based on energy conservation theory. In this approach, a large number of original particles are aggregated into coarse-grained particles while preserving the overall dynamic characteristics of the particle assembly. Scaling laws for contact forces, adhesive forces, and fluid–solid interaction forces after coarse-graining are derived, and a coupled coarse-grained discrete element method–computational fluid dynamics (CGDEM-CFD) framework applicable to mixed fiber–proppant systems is established to systematically investigate the settling behavior of fiber–proppant clusters. Based on the proposed model, the settling process of clusters under different coarse-graining conditions is simulated, and the evolution of cluster morphology, settling velocity, and pore structure is analyzed. The results indicate that fibers can form stable network structures among proppant particles, significantly increasing the characteristic size of the clusters and effectively suppressing their settling velocity. Meanwhile, the adopted coarse-graining method can substantially reduce the number of simulated particles and markedly improve computational efficiency while maintaining computational accuracy. The proposed method provides an effective tool for the efficient simulation of solid–liquid two-phase flows involving complex-shaped particles and offers important theoretical guidance for optimizing hydraulic fracturing parameters involving fiber-laden proppants.