Behavior Analysis of Fine Temporary Plugging Agents and Fibers in Bridging Regions: Migration and Clogging

Temporary plugging and diverting fracturing enhances unconventional reservoir stimulation by creating 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 inadequately understood. This study develops a hybrid CFD-DEM method integrating resolved, semiresolved, and unresolved models. The method implements variable coupling precision for particles of different sizes within a unified fluid mesh, balancing the accuracy of the flow field solution and computational efficiency. Based on this method, the effects of particle size, concentration, and shape on the macroscopic transport and clogging behavior of diverters in the bridging skeleton are investigated. Furthermore, the sealing layer formation process is analyzed across multiple scales, from mesoscale clogging evolution to microscale interparticle contact characteristics. The results demonstrate that fine particles initially migrate rapidly along preferential flow paths within the bridging skeleton. As injection proceeds, smaller particles exhibit greater mobility and are less prone to clogging at pore throats, whereas larger particles tend to accumulate and form size-dominated clogs, significantly hindering subsequent particle transport. In mixed particle systems, small particles help alleviate clogging at pore throats and promote a more uniform spatial distribution, while large particles facilitate the formation of dense local clogging structures. Increasing particle concentration intensifies competition at pore throats and accelerates the development of dense and stable clogging in the lower part of the skeleton. Although fibers are composed of small constituent particles, their high aspect ratio restricts migration, leading to retention near the skeleton entrance and the formation of extensive U-shaped clogging regions. At low concentration, the normal contact force distribution in fine particle clogging zones is highly anisotropic. In contrast, higher concentrations, mixed particle systems, and the presence of fibers all reduce this anisotropy, thereby enhancing the structural stability and sealing performance of the clogged regions. This study reveals multiscale mechanisms of tight sealing formation in fractures and establishes a theoretical foundation for optimizing temporary plugging and diverting fracturing techniques. Moreover, the developed hybrid CFD-DEM approach holds broader applicability in petroleum engineering scenarios involving fine powders or cross-scale particle transport.