The shape of the proppant is important because shape and size influence the final permeability through the fracture. A wide range of particle sizes and shapes will lead to a tight packing arrangement, reducing permeability/conductivity. A controlled range of sizes and preferential spherical shape will lead to greater conductivity. The roundness has been historically analyzed (2) using a visual, manual method based on the chart shown in the figure below, originally developed by Krumbein and Sloss. This method results in large subjective differences from operator to operator.
Chart for visual estimation of sphericity (y-axis) and roundness (x-axis)