Numerical simulation study of multi-cluster hydraulic fracture propagation in deep coal seams using the 3D lattice method

Deep coalbed methane (CBM) has become an increasingly critical target for exploration and development in recent years, with large-scale hydraulic fracturing being a key technology for achieving efficient extraction. However, the widespread development of cleat/fracture systems within coal seams significantly increases the complexity of fracture propagation. Furthermore, the varied horizontal stress differences (HSD) in deep coal seams pose significant challenges to fracture geometry control and uniform propagation. Therefore, this study develops a fluid–solid coupling hydraulic fracturing model for fractured coal seams using a three-dimensional lattice method according to the No.8 coal of the Benxi Formation in the Ordos Basin. The impact of stress difference, natural fracture interference, and engineering parameters on fracture propagation mechanisms are investigated. The results indicate that the HSD is a critical threshold determining the fracture propagation mode. Under the typical low HSD (4 MPa) condition, fracture propagation is dominated by natural fracture induction, forming high-tortuosity complex fracture networks, which is fundamentally different from the planar propagation under high HSD. Regarding engineering parameter optimization, cluster spacing exhibits a non-monotonic control on stimulation effectiveness. A spacing of 12 m is identified as the optimal window to balance interference and reservoir coverage. Additionally, an excessive number of perforation clusters triggers inhibition effects, reducing fracturing uniformity. This study enhances the understanding of hydraulic fracture propagation mechanisms in deep coal seams, offering a theoretical reference for optimizing fracturing engineering designs.