Numerical Simulation of Migration and Placement Law of Proppants in Rough Fractures

The rough and narrow fracture walls reduce the effective fracture volume of hydraulic fracturing, which greatly affects the migration and placement of proppants in the fractures and the effect of fracturing stimulation. Therefore, the self-correlated Gaussian distribution surface was established by Matlab, and the rough fracture surface was identified and analyzed with fractal theory. The bidirectional coupling of the computational fluid dynamics-discrete element method (CFD-DEM) was employed to build three-dimensional models of fractures with different roughness, and the deposition and migration process and law of different combinations of proppant diameters within the rough fracture channels were investigated. The research findings indicate that as the fractured surface transitions from smooth to rough, proppant plugging becomes more evident. Under the influence of gravity, small-sized proppants (ratio of diameter to fracture width of 0.3) exhibit better migration capabilities but struggled to ensure the near-wellbore supporting effect. The area covered by large-sized proppants (ratio of diameter to fracture width of 0.8) increase by 158.1%, but the proppant is blocked near the fracture end, affecting subsequent proppant migration to distant areas. Therefore, the recommended ratio of diameter to fracture width is 0.4. For the sand addition method with combined particle diameters, it is recommended to inject small-sized sand first and then large-sized sand to ensure the proppant migration distance and efficiency. The research outcomes contribute to a better understanding of the influence of fracture roughness on proppant migration within fractures, providing important guidance for optimizing fracturing design and operation parameters.