Clogging and Unclogging of Fine Particles in Porous Media: Micromechanical Insights From an Analog Pore System

Abstract

Pore clogging and unclogging in porous media are ubiquitous in subsurface hydrologic processes, which have been studied extensively at various scales ranging from a single pore to porous‐medium samples. However, it remains unclear how fluid flow, particle rearrangement, and the arching effect typical of cone‐shaped pore geometry interact and how they are captured by a pressure drop model at the macroscopic scale. Here, we investigate the pore‐scale feedback mechanisms between fluid flow and pore clogging and unclogging using a fully resolved fluid‐particle coupling approach (lattice Boltzmann method‐discrete element method). We first propose to use a truncated‐cone pore to represent realistic pore geometries revealed by X‐ray images of prepared sand packing. Then, our simulations indicate that the pore cone angle significantly influences the pressure drop associated with the clogging process by enhancing particle contacts due to arching. A modified Ergun equation is developed to consider this geometric effect. At the microscale, clogging can be explained by the interparticle force statistics; a few particles in an arch (or a dome) take the majority of hydrodynamic pressure. The maximum interparticle force is positively proportional to the particle Reynolds number and negatively associated with the tangent of the pore cone angle. Finally, a formula is established utilizing fluid characteristics and pore cone angle to compute the maximal interparticle force. Our findings, especially a modified pressure drop model that accounts for pore geometry resistance, provide guidance for applying pore‐scale models of clogging and unclogging to large‐scale subsurface fines transportation issues, including seepage‐induced landslides, stream bank failure, and groundwater recharge.

Fluid‐Driven Particle Migration and Its Impact on Hydraulic Transmissivity of Stressed Filled Fractures

“…Although the hydraulic pressure at the fracture inlet remains below 450 kPa throughout the experiment, the hydraulic gradients across the fracture vary from 70 to 442 due to the small fracture size, which may surpass natural conditions. Nonetheless, it should not be inferred that the particle migration and hydraulic transmissivity observed in this study are exclusive to such high hydraulic gradients because the fluid drag force determining the migration behavior of particles essentially depends on the flow velocity of the fluid surrounding the particles (Deal et al, 2023;Y. Yin et al, 2024).…”

“…Upon a further increase in the hydraulic gradient, which reaches a level capable of mobilizing the particles comprising the soil skeleton, erosion within the fracture regains its dominance and intensifies, marking the transition of particle migration to the EE phase (inset iii in Figure 7a) and ultimately to the SF phase (inset iv in Figure 7a). It is important to highlight that existing studies on particle migration behavior within porous media typically assume that the coarse particles constituting the soil skeleton are immobile (C. Han & Kwon, 2023;Yin et al, 2024). Consequently, the observed patterns of particle erosion and pore clogging, modulated by hydraulic gradients, have not been adequately addressed in the literature.…”

“…In the CO phase (130 < I ≤ 250), R i drops significantly for all particle sizes, suggesting a reduced impact of increasing hydraulic gradient on particle erosion. This is attributed to larger hydraulic gradients facilitating the movement of coarser particles, which leads to enhanced clogging via sieving and bridging (R. and thus inhibits particle migration (Xia et al, 2023;Y. Yin et al, 2024).…”

“…This discrepancy with practical scenarios is evident. Particle migration driven by fluid flow through granular media is prevalent in natural geological formations and hydraulic structures, particularly in highpressure fluid flow contexts (C. Han & Kwon, 2023;Y. Yin et al, 2024;Zhou et al, 2019).…”