A STUDY ON NON-UNIFORM PROPAGATION OF MULTI-CLUSTER HYDRAULIC FRACTURES IN DEEP SHALE RESERVOIRS BASED ON A TWO-LEVEL FLOW DISTRIBUTION MODEL

Non-uniform initiation and propagation of multi-cluster hydraulic fractures in deep shale formations represent a major challenge that restricts efficient reservoir stimulation. The uniformity of fracture propagation is influenced by multiple factors, including flow friction, perforation erosion, and stress interference between fractures during hydraulic fracturing operations. In this study, a two-level flow distribution model based on the equivalent electrical circuit method was developed, representing the "wellbore-perforation cluster-left/right fracture wings" system. The model incorporates along-wellbore friction, perforation friction, fracture flow resistance, perforation erosion, and inter-cluster stress interactions. Coupled with the discrete element method (DEM) and calibrated using well log interpretations and laboratory test results, the model was employed to systematically investigate fracture propagation behavior in the Wufeng-Longmaxi Formation shale of the Sichuan Basin under different combinations of cluster number, cluster spacing, fluid viscosity, and injection rate. The study reveals the mechanisms underlying non-uniform fracture propagation in deep shale formations. The results indicate that, under a constant total injection rate, increasing the number of clusters leads to a transition from uniform to non-uniform inter-cluster fracture propagation, accompanied by asymmetric growth between the left and right wings of individual fractures. Increasing the injection rate enhances the driving force for fracture propagation, mitigates stress interference, and helps reduce both inter-cluster non-uniformity and intra-cluster asymmetry. Both excessively low and high fluid viscosities tend to aggravate fracture non-uniformity, though through different dominant mechanisms. Therefore, selecting an appropriate fracturing fluid viscosity is essential for controlling fracture height and minimizing near-wellbore stress perturbations and flow allocation imbalances. This research provides theoretical support and engineering guidance for optimizing fracturing parameters and developing fracture control strategies in deep shale reservoirs.