Propagation law of fractures in deep shale gas reservoirs considering the influence of interlayers and interfaces

Unconventional shale gas reservoirs are a vital component of oil and gas exploration and development, and hydraulic fracturing is typically required to enhance reservoir permeability. Deep shale reservoirs are characterized by numerous thin layers, complex layer interfaces, and significant property variations between layers, which severely restrict the process of hydraulic fracture propagation. Currently, the propagation patterns of hydraulic fractures under the influence of interlayers and interfaces with varying properties remain unclear. In this study, based on the primary characteristics of deep shale reservoirs in the southern Sichuan Basin, a three-dimensional (3D) fracture propagation model that incorporates the effects of interlayers and interfaces was established using the discrete lattice method. Numerical simulations were conducted to investigate hydraulic fracture propagation under various conditions of interlayer thickness, interface strength, and dilation angle. The study found that interlayers and interfaces hinder the vertical propagation of hydraulic fractures, with shear failure occurring primarily at the interfaces and tensile failure dominating in the surrounding matrix. With the increase in interface tensile strength, friction angle, and cohesion, the hydraulic fracture changes from propagating along the interface to penetrating the interface. When the interface tensile strength is 5 MPa, the friction angle is 35°, and the cohesion is 10 MPa, the hydraulic fracture penetrates the interface significantly, with only a small part propagating along the interface. As the interface dilation angle increases, the ability of hydraulic fractures to penetrate the interface gradually weakens. When the interface dilation angle is greater than 10°, the hydraulic fracture is completely blocked. The research results can provide a theoretical basis for controlling fracture height and hydraulic fracture layer-crossing during on-site fracturing operations, contributing to efficient fracturing and reservoir stimulation.