Understanding characteristics of gravitational particle settling using particle image velocimetry

A significant challenge to hydraulic fracturing is premature particle settling and uneven particle distribution in a formation during injection. Even though various research work were conducted on particle transport, gaps still exist in the fundamental proppant–proppant interaction mechanisms. This study utilizes an experimental approach to understand proppant interactions during gravitational settling in various test conditions. High-speed imaging coupled with particle image velocimetry (PIV) was implemented to provide a space and time-resolved investigation of multi-proppant interactions. The multi-perspective experimental study uncovered the coupled effect of viscosity and multi-particle mix ratio on slurry velocity. The PIV analysis highlights unique agglomeration and particle interactive patterns. The results indicate that the mix ratio has a significant effect on proppant interactive behavior and settling characteristics, especially as the solution viscosity increases. This conclusion was drawn from observing no signs of agglomeration in the low viscosity regime, although slight differences in proppant interactions were noted as the mix ratios were altered. On the other hand, the intermediate regime demonstrates formed agglomerates with unique patterns for different viscosity and mix ratios. The observed patterns were quantified using both velocity and proppant concentration analysis. Finally, the results indicate the existence of a reduced velocity condition at a given viscosity and particle mix ratio.