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

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.