This paper presents experimental results and analysis of proppant flow and transport in narrow fractures. Proppant is granular material used in hydraulic fracturing for permeability enhancement of geo-reservoirs. Proppant-fluid slurry is pumped into a fracture network to prevent fracture closure. Insufficient proppant transport or clogging occurs frequently in practice. The fundamental behavior of flow and transport of dense slurries and proppant placement is still poorly understood, and current practices involve simple empirical predictive formulas, which lead to trial and error with a high rate of failure. Experiments investigate flow and transport of slurries with volumetric concentrations up to 60% in a bi-wing fracture. Particle image velocimetry (PIV) serves for obtaining the velocity field of dense particulate flows from video capture. The effect of parameters such as flow rate, grain size, fluid viscosity, aperture and particle concentration on slurry flow regime is analyzed. Sediment flows regimes vary from pure settling to suspended particle transport. In wider slots at lower flow rates and high volumetric concentrations of medium sand the transport is limited and the applied procedure failed to carry significant amounts of proppant far into the slot. The velocity and slurry transport tapers off in the fracture depending on slurry properties and injection conditions. For high viscosity fluids and very fine sand, and extremely slow-flowing suspension of particles is observed. The observations suggest that significantly different mechanisms of sediment transport dominate during particulate multiphase flow depending on slurry properties and geometric conditions.

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