Experimental Evaluation of Turbulent Flow and Proppant Transport in a Narrow Fracture

Abstract

We present results of an experimental investigation of turbulent flow of proppant and fluid slurries in narrow smooth fractures. Proppant is a small granular material, which is introduced into hydraulic fractures to keep them open for a long-term geo-reservoir function. Proppants are used in geothermal reservoirs wherein permeability enhancement relies on tensile fracture propagation, and shearing of existing fractures is not a dominant mechanism. Such georeservoirs occur in sandstone geological formations or on the boundary between sedimentary and igneous rock masses. Our laboratory experiments are performed using Plexiglas and 3D printed narrow fracture zones. A progressive cavity pump injects proppants mixed with carrying fluids in varied volumetric concentrations at varied flow rates. Several different proppants are used. Our results indicate that turbulence is a decisive factor in progression of the slurry into a fracture system. However, turbulent motion of dense particle phase slurries is not yet well understood. Smaller particles respond well to higher flow rates and are carried over the bed of proppant in turbulent swirls. Therefore, the slurry consisting of smaller sand particles does not form a large proppant bed and is transported further into the fracture system. Fracture aperture, fluid viscosity, and flow rates are also evaluated against turbulent slurry motions.