Settling and hydrodynamic retardation of proppants in hydraulic fractures

An experimental and modeling study was undertaken to investigate proppant settling and retardation in hydraulic fractures. Experiments were conducted in a fracture flow cell for Newtonian fluids as well as shear thinning fluids with varying viscosities. New empirical and analytical models for proppant transport and settling in hydraulic fractures were developed. These models can be used in any hydraulic fracture simulator. The proppant settling models developed account for changes in the settling velocities and rheology caused by fracture walls, proppant concentration, turbulence effects due to high fluid velocities and inertial effects associated with large relative velocities between the proppant and the fluid. Proppant velocity relative to the fluid in the direction of flow is affected by the fracture walls and can result in significant reduction in the proppant transport. A model was developed to estimate the proppant retardation (ratio of particle velocity to the fluid velocity) due to these effects. All these correlations have been incorporated into a fully 3-D hydraulic fracture code, UTFRAC-3D. The impact of these factors on created fracture geometry is shown for the first time.