To address the limitation of conventional smooth parallel-plate models，namely neglecting the influence of roughness on proppant transport，this study establishes a fracture geometry model based on fractal theory to embody actual reservoir roughness characteristics，where the Weierstrass-Mandelbrot function is modified using measured rock-wall profile data. The coupled computational fluid dynamics and discrete element method （CFD-DEM） is employed to simulate proppant migration and post-fracturing flowback，with a focus on the effects of the injection port number，proppant concentration，and particle size combination. The results indicate that in the case of single-port injection，fracturing fluid energy is concentrated to deliver a maximum equilibrium proppant bank height of 3.25 cm and the lowest flowback rate. When the proppant concentration increases from 8% to 11%，the proppant bank height rises from 2.60 cm to 3.28 cm，accompanied by a corresponding decrease in the flowback rate of proppants. For a particle size combination of 70/140 mesh，40/70 mesh，and 20/40 mesh at a mass ratio of 1：6：3，the equilibrium proppant bank height reaches 3.28 cm，and the proppant retention rate reaches 97.64%. It is revealed that rough-wall undulations induce localized vortex zones，increase the resistance to particle settling，and promote the formation of inter-particle force chains，thereby significantly enhancing proppant bank stability and near-wellbore placement efficiency. The proposed fractal-modified fracture model and the CFD-DEM coupling approach effectively capture the nonlinear effects of wall undulations on particle transport，providing theoretical support for optimizing proppant placement strategies in shale oil hydraulic fracturing.