Insights into the flow characteristics during hydraulic fracturing

This paper presents a numerical model to study fracture propagation during water-based hydraulic fracturing. To address the computational challenges associated with the numerical model, the proposed approach employs a set of overlapping spheres arranged in a monolayer to construct a porous specimen containing pre-existing cracks. The fluid-filled cracks represent various stages of initiation and propagation of fluid-driven fracture. The high-pressure fluid flow within the fractures is considered under isothermal conditions. Unlike the conventional focus on rock fracture analysis, the presented approach focuses on flow characteristics during fracture growth. The main objective of the presented study is to provide a detailed description of the computational fluid dynamics (CFD) aspects of fracture propagation during hydraulic fracturing to aid in calibration and validation of simplified discrete element method (DEM) models coupled with CFD representing this phenomenon. Experimental validations performed in previous studies support the model's reliability, making it useful in particular for calibration and validation of coupled 2D DEM-CFD models constructed from one layer of spheres. Obtaining experimental data for such cases is practically challenging, and the proposed model addresses the lack of reliable experimental data for hydraulic fracturing. To achieve this, representative specimens are designed, accurate simulations are conducted and precise assessments of the results are performed. Key variables such as density, pressure, velocity, porosity, and permeability were measured to facilitate the validation and calibration of future DEM-CFD studies.