Mechanisms and Influencing Factors of Fracture Propagation in Thin Interbedded Sandstone-Mudstone Reservoirs

To address the challenge of vertical fracture breakthrough through interlayers during fracturing in the thin interbedded sandstone-mudstone tight oil reservoir of the Gao5 Fault Block in the Jidong Oilfield, Bohai Bay Basin, this study developed a fluid-solid coupling fracture propagation model using a 3D discrete lattice method. Field-scale vertical well fracturing numerical simulations were combined with single-factor sensitivity analysis experiments to systematically investigate the influence of reservoir thickness, interlayer stress difference, elastic modulus contrast, and operational parameters on fracture geometry. Results indicate that vertical fracture propagation is synergistically controlled by the mechanical parameters of the reservoir and interlayers: the breakthrough probability significantly decreases when the interlayer thickness exceeds 3 m; increased interlayer stress difference (>10 MPa) suppresses vertical extension and induces lateral slippage; and elastic modulus contrast indirectly influences path selection through interfacial stress concentration. For operational parameters, increased pumping rate significantly enhances fracture height growth, while elevated viscosity (>50 mPa·s) promotes fracture penetration through interlayers. Fracture propagation exhibits a stepwise growth pattern, primarily governed by the fracture tip blunting effect and lithological interface stress shielding effect. Innovatively applying the 3D discrete lattice method, this study reveals the stepwise propagation mechanism in thin interbeds and establishes fracture geometry prediction charts based on reservoir thickness, interlayer Young’s modulus ratio, and stress difference. Additionally, it identifies a critical pumping rate threshold (3.2 m3/min) for regulating interlayer penetration, providing a quantitative basis for optimizing fracturing designs in thin interbedded reservoirs. These findings hold significant engineering implications for improving stimulation efficiency and reducing development costs in unconventional oil and gas reservoirs.