This paper shows results and analysis of experimental investigation for coarse, medium and fine sand flow and transport into narrow slots. The presented research is conducted within a context of proppant flow and transport in geo-reservoirs during placement into fractures. Proppant is granular material which is placed into hydraulic fracture for propping the fracture open and enhancing production in geo-reservoirs. The experimental investigation presented in this paper contributes to better understanding of proppant-fluid slurry flow and transport in narrow fractures and complement current empirical relationships derived from wider slot experiments. At higher proppant concentrations in narrow and constrained fractures inter-particle and particle-wall contact interactions affect the general slurry flow and transport, phase motions and their relationships. In this work, various volumetric concentrations of coarse, medium and fine silica sands are injected into a relatively narrow fracture under different flow rates and using Newtonian carrying fluids. Results indicate and quantify the significance of particle size in a narrow slot on various flow regimes observed. Sediment transport theories are used to quantify flow regimes and investigate whether the Rouse number can be used to correctly predict the flow regime in a narrow fracture. Presence of turbulence in slurry motion is evaluated towards optimal flow and transport outcomes. The presented results will aid geothermal and petroleum engineers to better design proppant transport, increase utilization of sustainable sand materials and better understand fundamental flow and transport of dense-phase slurries in narrow fracture zones.