Regulation of proppant transport and placement in rough fractures by adhesive flexible fibers

Fibers are key materials for regulating the transport and placement of proppants, but their mechanism of action remains unclear. In this study, a solid–solid–liquid three-phase coupled computational fluid dynamics and discrete element method approach was developed to incorporate adhesive flexible fibers, enabling the simulation of their regulatory mechanisms in proppant transport and placement within rough fractures. The results show that fibers intertwine into a network structure that drags and wraps adjacent particles, allowing proppants to escape isolated migration and forming a novel and efficient “fiber–proppant cluster cooperative transport” mode. Adhesion promotes cluster formation and prevents fiber overflow, while velocity differences inside and outside clusters cause uneven drag and shear failure. When forces reach equilibrium, stable clusters migrate toward the fracture tip. Greater fracture wall roughness leads to more complex placement patterns but has little effect on filling ratio. With increasing fiber concentration and length, the settling slope angle first decreases and then increases, indicating optimal values that scale with proppant particle size. Higher fluid velocity and viscosity further reduce the settling slope angle. These findings provide theoretical guidance for developing novel fiber fracturing materials and optimizing fracturing parameters.