Modeling Hydraulic Fracture Network Propagation in Fractured Shale Reservoirs Using the Extended Finite Element Method

Summary In the research on hydraulic fracturing network evolution in fractured shale reservoirs, there are several key issues. For instance, it is generally assumed simplistically that the interfacial frictional properties of natural fractures (NFs) govern the propagation direction of fractures, overlooking that real rocks are typically aggregates of different minerals and may exhibit a certain degree of cementation. To address the comparative analysis of two types of fractures within the same parameter framework in this study, we established a 2D hydraulic fracturing model based on the extended finite element method, developed a new intersection criterion for cemented fractures, elucidated the mechanism of the fracture deflection phenomenon, and addressed the inherent limitations of this method in handling fracture intersections. Subsequently, the numerical model was used to analyze how different types of NF clusters influence the fracture network morphology. The results show that a small horizontal stress difference, high approaching angle, and small fracture interface friction coefficient are more conducive to the formation of fracturing networks in frictional NF groups. Cemented NF groups require small cementation strength, high approach angles, and higher injection rates to form complex fracture networks, which balance differences in energy release rates between the upper and lower halves of NFs. Additionally, the more concentrated the distribution of NFs, the more likely they are to intersect with hydraulic fracture (HF) branches and form complex fracture networks. When the geometric characteristics and spatial distribution of NFs are consistent, the fracturing networks formed in formations with frictional NFs exhibit significantly higher complexity than those in cemented formations. Stress interference between branched fractures not only alters their mutual propagation trajectories but also affects fracture opening conditions, and the distribution position of NFs exerts a critical impact on fracture network formation. This study provides theoretical support for optimizing fracture network stimulation in hydraulic fracturing operations for fractured shale reservoirs.