Mechanisms of Proppant Deposition and Distribution in a Fracture during Impulse Injection

The uneven particle distribution has posed a significant challenge to hydraulic fracturing operational efficiency. Previous investigations aimed to uncover the complex proppant behavior during injection. However, there still exist gaps in the fundamental proppant–proppant colliding interaction mechanisms and proppant deposition. The vigorous proppant–proppant and proppant-wall colliding behavior pose a challenge in understanding the overall slurry behavior due to the formation of turbulent eddies and vortices, especially during impulse injection in fractures. This study aims to shed light on proppant deposition behavior during impulse injection in various test conditions, namely inclusive and exclusive of gravitational effects. The injection was conducted using a microfracture model positioned in horizontal and vertical configurations to control the gravitational effect on deposition. The coupled application of high-speed imaging and particle image velocimetry (PIV) provided a space and time-resolved investigation of the flow patterns in the three-way proppant-fluid-fracture complex interaction problem. Additionally, the study utilized binary thresholding to quantify the coupled effect of injection solution viscosity and fracture angle on the deposition mechanisms, especially the uneven proppant distribution. The PIV investigation highlighted various unique vortex formation patterns at different fracture angles and solution viscosities. The horizontal (minimal gravitational effect) pure water (control-no viscosity alteration) experiments yielded a chaotic and unrepeatable deposition process with a spraying effect at the fracture junction. As the solution viscosity increased, injection stability was achieved by observing proppant clustering behavior indicative of potential fracture clogging behavior at the highest solution viscosity. No observable patterns of a specific proppant ratio deposition were made in the horizontal experiment. On the other hand, the experiments under gravitational effects indicated a minimal difference in deposition between pure water and the intermediate viscosity solution. As the solution viscosity was increased, particle agglomeration was observed, coupled with increased fracture deposition. Lastly, a few experiments highlighted higher deposition in downstream fractures when compared to upstream, which agrees with previously published numerical work.