This paper presents the results of an experimental study of dense sand particles’ settling micromechanics in narrow smooth and rough fractures. Particle Image Velocimetry (PIV) is used for the analysis of velocities of individual particles and groups of particles and their relative paths, collisions, and agglomerating in viscous Newtonian fluid. The displacement vectors obtained through PIV analysis show the movements and velocities of individual and groups of particles and the global velocity trends of the observed area. Experiments were conducted in a relatively narrow 2-mm slot compared to the main particle size of 0.66 mm across. Smooth and rough fracture walls are considered, in which acrylic plates and 3-D–printed hydraulic fracture replica were used. The measured results from this experimental study give new insights into the effects of particle and agglomerate size and shape as well as fluid dynamic viscosity on slurry settling velocity. It was found that an increase in fluid dynamic viscosity promotes the formation of larger agglomerated particles of sand, which, in return, affect overall slurry settling velocity. Observations from rough fracture wall experiments yielded significantly different slurry behavior, with increased erratic particle motions and fewer agglomerations compared to the smooth, idealized fracture walls. Experimental results give new insights into slurry settling in narrow fractures, which has applications to proppant settling in fractures for the oil, gas, and geothermal industries.