Evaluating the stability and volumetric flowback rate of proppant packs in hydraulic fractures using the lattice Boltzmann-discrete element coupling method

The stability and mobility of proppant packs in hydraulic fractures during hydrocarbon production are numerically investigated by the lattice Boltzmann-discrete element coupling method (LB-DEM). This study starts with a preliminary proppant settling test, from which a solid volume fraction of 0.575 is calibrated for the proppant pack in the fracture. In the established workflow to investigate proppant flowback, a displacement is applied to the fracture surfaces to compact the generated proppant pack as well as further mimicking proppant embedment under closure stress. When a pressure gradient is applied to drive the fluid-particle flow, a critical aperture-to-diameter ratio of 4 is observed, above which the proppant pack would collapse. The results also show that the volumetric proppant flowback rate increases quadratically with the fracture aperture, while a linear variation between the particle flux and the pressure gradient is exhibited for a fixed fracture aperture. The research outcome contributes towards an improved understanding of proppant flowback in hydraulic fractures, which also supports an optimised proppant size selection for hydraulic fracturing operations.