Toward a fundamental understanding of the impact mechanisms of analog proppant-clastic rock systems through numerical analysis

The understanding of the collision behavior of proppants with clastic rocks comprises an important step to model, at a larger-scale, problems involving hydraulic fracturing, especially during the stage of high-pressure injection of fluids with proppants to initiate rock fracturing. This paper presents a multiscale study on the interaction problem of proppant simulant (impactor) colliding on the surface of a block (analog rock) by performing 3-dimensional discrete element analysis. Three variants of the block material representing strong, medium-strength and weak clastic rock are simulated considering a variation in bond and contact stiffness as well as bond strength using the linear parallel bond contact model. The interaction between the rock (made of bonded particles) and the impactor (proppant particle) was defined by the Hertz-Mindlin contact model which truly represented the force-displacement response for a grain-block system. A parametric study was conducted to assess the effect of the size of the impactor and the velocity at collision on the damage characteristics of the base rock. It was found that there exist significant differences in the impact response when different impactor and rock attributes are considered. Emphasis was placed in the analysis of macroscale parameters such as stress and energy transfer, mesoscale parameters such as penetration depth and contact formation, as well as microscale parameters such as contact force network and fracture network.