Coupled CFD-DEM modeling of fine particles and fibers migration and clogging mechanisms in bridging regions

Abstract

Temporary plugging and diverting fracturing enhances unconventional reservoir stimulation by forming a tight sealing layer through the bridging and filling of diverters in fractures. The tightness and pressure bearing capacity of the sealing layer are governed by the clogging efficiency of fine particles and fibers in the bridging region. However, the clogging mechanism within the pores of coarse particles after bridging remains poorly understood. This study employs a hybrid CFD-DEM method to investigate the migration and clogging behavior of diverters in a bridging skeleton. The results indicate that fine particles initially migrate rapidly through dominant flow paths, while fiber movement is restricted by their high aspect ratio and mainly localized at the skeleton entrance. In single-size particle systems, larger fine particles form size-dominated clogs at pore throats, with clogging ratios increasing with both particle size and concentration. Mixed particle systems exhibit a more uniform clogging distribution and reduced sensitivity to concentration, owing to the cooperative filling of pore spaces. Fibers exhibit high clogging ratios under all conditions due to their tendency to attach and entangle on bridging particle surfaces. In single-size systems, particles whose sizes match pore throats and higher concentrations yield denser, less permeable sealing layers. Mixed particle systems result in even lower normalized permeability via synergistic filling. Fiber-induced clogging leads to the lowest permeability, forming continuous covers at pore entrances. For clogging stability, fine particles exhibit a “high contact number-high clogging ratio” pattern, while fibers display a “moderate contact number-high clogging ratio” pattern with fewer contacts required for retention. At low concentration, fine particles exhibit pronounced anisotropy in normal contact forces distribution, while mixed particle systems and fibers both reduce this anisotropy and promote a more uniform force network. This study clarifies multiscale sealing mechanisms and provides a theoretical basis for optimizing temporary plugging and diverting fracturing.