On the correlation between proppant addition strategy and distribution

Abstract

The proppant pumping schedule is critical in hydrofracking because it affects both fluid flow and proppant transport. In the study reported here, a validated CFD-DEM model was employed to study the impact of proppant pumping strategy on proppant transport in a rough rock fracture. Three injection sequences of multi-sized proppants were applied while varying other pumping parameters including injection velocity, the size of large proppants, and the concentration of large proppants. Both vertically and horizontally sheared rough, joint rough, and smooth fractures were adopted to enable a better understanding of the impact caused by fracture geometry. The results reveal that the variation in proppant distribution caused by adjusting the pumping sequence or a single pumping parameter is not absolute. Rather than pumping parameters, the final proppant distribution is governed directly by two competing effects caused by the alteration of proppant bridging effect. It was also found that the proppant volume retained in fractures is under-estimated if the CFD mesh size is too small to reach three times the particle size. The lateral conveyance of proppant could be enhanced by considering the Saffman lift force in CFD-DEM modeling. The results of this study shed light on proppant transport in hydraulic fractures under various addition strategies, which will assist the optimization of fracturing treatments in unconventional reservoirs.