Experimental Study of Proppant Settling in a Narrow Fracture Analyzed with Particle Image Velocimetry

This study presents results of an experimental study of the micromechanical proppant behavior during settling in both narrow smooth and rough fractures. This fundamental analysis seeks to better understand dynamics of particle interactions in a dense phase slurry on a small particle size scale, representing proppant settling in narrow hydraulic fractures. Particle Image Velocimetry (PIV) is used for analysis of velocities of individual particle and group particles and their relative paths, collisions and agglomerating in viscous Newtonian fluid. The displacement vectors show the movements of group of particles and global velocity trends of the observed area. The results from this experimental study indicate dependency of settling velocity on particle size and shape, as well as the dependency of different size of particle or agglomerate particles. The measured results, including vertical velocities and displacement vectors of singular particle and agglomerated particles, were compared with previously published theoretical and empirical relationships. It can be seen that forming of proppant agglomerates during settling, caused by frequent particle-particle and particle-wall collisions and interactions, changes the overall settling velocities predicted by the previous experiments in larger slots. The slurry settling velocity depends on the relationship between settlement, proppant concentration and occurrence of proppant agglomeration. This study also compares the different agglomerations in different fluid. This study presents the influence of proppant concentration and proppant agglomeration. The effect of wall can also been found when the concentration and agglomeration is high. In order to better understanding proppant settling in hydraulic fracture where mostly rough, the proppant settling in narrow slot with adding rough surface is also analyzed. By comparing experimental results of proppant settling in narrow slot with both smooth surface and rough surface, it can be found that the rough surface can diminish average settling velocity. The decreasing of proppant concentration and agglomeration is also found in this study