Effect of Natural Fracture Clusters on Hydraulic Fracture Propagation in Fractured Reservoirs: A Numerical Simulation Study

The presence of a large number of natural fracture clusters in fractured reservoirs has a significant impact on fracture propagation during hydraulic fracturing. A two-dimensional fluid–solid coupled hydraulic fracture intersection extension finite element model was established considering the coupling between the deformation of rock and the fluid flow inside the fracture as well as the interaction between natural fracture (NF) and hydraulic fracture (HF). The results indicate that when HF intersects NF with a high approach angle at a low horizontal stress difference, HF tends to pass through NF directly, and vice versa, HF tends to activate NF; with the increase of horizontal stress difference, the fracture as a whole extends in a zigzag shape along the direction of maximum principal stress. As the NF angle is higher, HF is prone to divert to activate the NF and the fracture extends in a step-like shape along the NF, and the higher the NF angle the straighter the fracture is, and the greater the fracture initiation pressure. The higher the injection rate, the more HF tends to penetrate the NF, and the straighter the HF morphology. The fracturing fluid viscosity has less influence on the expansion of HFs, and the HF morphology is approximately similar. This study has certain theoretical guiding significance for clarifying the propagation path of hydraulic fractures under natural fracture distribution and formulating the stimulation plan of fractured reservoirs.