Three-dimensional numerical simulation study on competitive propagation of dual-cluster fractures considering natural weak bedding planes

The presence of natural weak bedding planes significantly influences the propagation paths and network morphology of multi-cluster hydraulic fractures in shale reservoirs. Based on the ABAQUS finite element software, this study established a three-dimensional numerical model for competitive propagation of dual-cluster fractures considering a single natural weak bedding plane. The model comprises two hydraulic fractures (HF1, HF2) and one natural weakplane (NF1). Cohesive elements were employed to simulate the initiation and propagation behavior of fractures and the weakplane, with the interaction between fractures and the weak plane judged based on criteria of interfacial tensile strength and fracture toughness. Through simulation calculations, the influence laws of key parameters such as cementation strength, horizontal in-situ stress contrast, and fracturing fluid injection rate on the competitive propagation mechanisms of dual-cluster fractures and fracture network complexity were analyzed. The results indicate that an increase in the cementation strength of the weak plane inhibits its communication, which is detrimental to the formation of complex fracture networks. An increase in the horizontal in-situ stress contrast promotes fracture propagation along the direction of the maximum principal stress and alleviates inter-cluster interference. An increase in the fracturing fluid injection rate helps balance the propagation of the dual-cluster fractures, but excessively high rates may lead to uncontrolled fracture height growth. This study provides a theoretical basis for the optimal design of dual-cluster fracturing in reservoirs containing weak planes.