Influence of particle size and density on transport dynamics in fractured media: a numerical simulation study

Efficient particle transport within fractures is necessary in oil, gas, and geothermal reservoirs, as it governs fracture conductivity and well performance. Considering the dual challenges of proppant placement during hydraulic fracturing and particle-mediated contamination in fractured aquifers, the current study numerically investigates the particle transport in rough and smooth-walled fractures. Time-dependent fluid flow study governed by the Navier–Stokes equation coupled with a Lagrangian particle-tracing model were performed in a 3D fracture, and 28 scenarios were elaborated with varying particle sizes from 1 to 10 µm, densities, flow velocities, and the fracture geometry. Five thousand particles were randomly injected at each sample’s inlet and subjected to drag and gravitational forces. No slip boundary conditions were set for the upper and lower fracture walls for fluid flow, and a freeze boundary condition was used in the particle tracing simulation. Results showed that when the fractal dimension Df> 0, it creates a non-uniformity in the velocity distribution of the fluid, promoting particles to travel within the centerline and resulting in a random distribution of the plume, accompanied by an early arrival of some particles in all the tested scenarios. Roughness enhances particle retention compared to a smooth fracture. The retention is influenced mainly by both particle size and density. When particle size and density increase, the recovery rate decreases due to the settling effect. A similar attenuation was observed in reducing the flow velocity when larger and denser particles (dp > 4 µm) experienced no transport and were deposited near the injection area.