Micromechanical Modeling of Proppants for Hydraulic Fracturing

The durability of hydraulic fracture stimulation is a major requirement for the success of fossil fuel recovery from rock formations with low permeability such as gas-shale. To improve this property, proppants are generally used to hinder the closure of fractures and promote higher fluid conductivity. The efficacy of proppant placement, however, depends among various things also on their mechanical response under high compressive stresses. 3D compression simulations were performed in this study using the distinct element method (DEM) to investigate the interaction between proppants and rock formation, giving emphasis to the role of the crushing resistance of proppant packs. To capture the size-dependence of the particle strength, proppants were modeled by bonded agglomerates with strength assigned randomly via a Weibull statistics. The stress-strain behavior and particle size evolution of specimens characterized by different packings were then studied numerically. The results revealed that packings consisting of multiple layers can sustain higher stresses and producing considerably less fines compared to mono-layer packings subjected to the same extent of fracture closure. Such analyses show that DEM modeling has considerable potential to incorporate the size-dependence of grain fracture processes, i.e. a key element to evaluate alternative types of proppants and select an optimal mixture for site-specific stress conditions.