Simulation research of proppant flowback and control method after hydraulic fracturing based on CFD-DEM

Abstract

The proppant flowback after hydraulic fracturing has long existed in reservoir or enhanced geothermal systems. This not only reduces fracturing efficiency and damages equipment, but also generates solid waste. Due to the unclear understanding of the proppant flowback mechanisms, the control measures effectiveness is highly uncertain. This paper established a model that considers the synchronous changes of fracture closure and flow field based on the CFD-DEM. Numerical simulation research of near-well fractures including perforation was conducted. The results show that particles near and above the perforations are more prone to flowback. The critical fracture width to particle diameter ratio (w/d) for uniformly sized spherical particles is 2.55. Controlling the flowback velocity within the fracture to below 0.01 m/s allows the particles to form stable bridges. Non-spherical particles and particles with non-uniform diameters have less flowback and smaller changes in fracture width. For particles with non-uniform diameters, the minimum particle diameter is the main factor determining the particle flowback ratio. The more evenly the proportion of particles of different diameters is distributed, the stronger the ability of the proppant to resist the fracture closure. Particles with a larger size distribution range have a lower flowback ratio and a wider propped fracture width. Rod-shaped particles effectively resist the pressure of fracture closure, maintaining a larger fracture width. Perforating in the upper part of the reservoir, using low-viscosity fluids to reduce the near-well fracture width, filling the near-well fractures with large-sized, wide size distribution (such as 20/70-mesh) or non-spherical particles (such as rod-shaped proppant) could help alleviate the proppant flowback.