Numerical simulation of fracture propagation in Sand conglomerate reservoir under 3D lattice element method

• This study integrates three-dimensional discrete lattice theory, fracture propagation criteria, and synthetic rock mass methodologies to establish a 3D hydraulic fracturing model for sand conglomerate reservoirs. • This study establishes a single gravel model and a multiple gravel model, and selects two hydraulic fracturing experiments with different gravel grain sizes and distributions of clastic rocks to validate the numerical model. • Based on a single gravel model, this study investigates the behavior of fracture propagation when encountering gravel. • Based on multiple gravel models, this study investigates the behavior of fracture propagation when encountering multiple gravels and different construction parameters. Sand conglomerate reservoirs are vital global oil and gas resources, playing a crucial role in petroleum exploration and development. However, due to the inherent complexity and heterogeneity of sand conglomerate reservoirs, accurately predicting and controlling the propagation of hydraulic fractures and fluid flow patterns during hydraulic fracturing is challenging. Therefore, numerical simulation studies on hydraulic fracture propagation in sand conglomerate reservoirs are of substantial practical and theoretical importance. This study integrates the 3D discrete element method (DEM) with fluid-solid coupling and synthetic rock mass technique to develop a numerical model for hydraulic fracture propagation, systematically investigates the mechanisms influencing fracture propagation, including gravel tensile strength, contact angle, shape, stress differential, gravel content, and engineering parameters such as injection rate, fluid volume, proppant concentration, and pad fluid ratio. Results indicate that gravels with low tensile strength promote fracture penetration, while high-strength gravels encourage fracture deflection or termination. When the contact angle is <60°, fractures propagate along the gravel surface; above 60°, penetration tendencies become significant. Gravel shapes (e.g., circular, square, diamond) significantly affect fracture bifurcation and tortuosity through localized stress distribution variations. Increased stress differential suppresses fracture deflection, whereas higher gravel content and larger grain sizes amplify fracture complexity. Among engineering parameters, elevated injection rates and fluid volumes enhance fracture propagation but exhibit threshold effects. The optimal sand ratio and pad fluid ratio are recommended at approximately 15 % and 40 %, respectively, to balance proppant placement efficiency and fracture stability.