Microparticle transport and clogging mechanisms in 3D complex rock fractures based on coupled lattice Boltzmann and discrete element method simulations

Microparticle transport in rock fractures is widespread in both natural and industrial settings, playing a crucial role in hydrocarbon production, geothermal extraction, and pollutant migration. Compared to macroparticles, microparticles exhibit unique transport characteristics due to significant microscale forces, such as adhesion, traction, and aggregation. However, the mechanisms governing microparticle transport, retention, and deposition in complex and narrow fractures under microscale forces remain unclear, which may lead to misjudgments of microparticle migration distance and clog conditions. In this study, we develop an analytical lattice Boltzmann method-discrete element method (LBM-DEM) coupling model that incorporates the retarded van der Waals force to accurately reproduce these processes. The accuracy is validated against experimental results of microparticle cluster settling, and the necessity of softening the Hamaker constant when calculating van der Waals forces is demonstrated. To examine the effects of aperture variations and surface undulations, we established two fracture models: planar fractures with variable aperture and rough fractures with constant aperture. Simulations indicate that in planar fractures, clogging is induced by particle clusters, with deposition in the narrowing segment serving as a precursor to clogging events. In rough fractures, clogging also occurs, but is caused by the monolayer adhesion of particles to the fracture surface. The van der Waals force increases the number of arch-forming particles in planar fractures, while in rough fractures, it reduces overall transport distance and enhances particle distribution heterogeneity. An increase in the narrowing segment angle weakens gravity-driven settling, accelerating fracture sealing. Higher roughness and concentration, as well as smaller apertures, promote large-scale clogging at the inlet and intensify preferential flow.