Research and application of hydraulic fracture height propagation based on 3D lattice method

The key of shale gas development lies in creating large-scale fracture networks through hydraulic fracturing to significantly enhance reservoir permeability. However, the traditional theory that bedding fracture activation plays a crucial role in fracture networks has been challenged by recent field tests in North America. This paper investigates the influence of interlayer rock mechanical properties and bedding plane characteristics on the interlayer penetration and propagation of hydraulic fractures using the 3D discrete lattice method. Such factors as interlayer stress contrast, elastic modulus variations between layers, bedding plane dip angles, bedding plane cohesion, vertical/horizontal stress contrast, injection rates, and fracturing fluid viscosity were analyzed. A quantitative evaluation chart for hydraulic fracture interlayer propagation was established. The results show: (1) As the elastic modulus of the upper barrier layer and lower interlayer increases, vertical propagation of hydraulic fractures becomes easier, with fracture height gradually increasing, leading to insights that differ from traditional theories. In field practices, high-modulus formations are often associated with high-stress values, which restricts interlayer hydraulic fracture propagation. However, the influence of elastic modulus might be misinterpreted from a lithological perspective. (2) With increased cohesion of bedding layers and reduced bedding dip angles, the characteristics of interlayer hydraulic fracture propagation become more pronounced, making it difficult to activate bedding fracture. Hydraulic fractures transition from "I-shape" to "Tu-shape" and "Feng-shape" patterns. (3) In mature development zones, as formation pressure depletes, horizontal stress contrast and vertical effective stresses increase. Subsequent infill wells fracturing operations face significantly higher difficulties in activating bedding fractures, leading to dominant interlayer propagation. Key factors affecting interlayer propagation were analyzed through single-factor orthogonal studies, establishing discrimination charts for interlayer propagation in laminated shale. During fracturing layer selection, lithological combinations and bedding characteristics should be comprehensively evaluated using the chart. On the basis of the rock mechanical and bedding features of Hongxing shale gas in Fuling area, the horizontal well target window was shifted from the previously geologically favorable sub-layer ③ to a geological + engineering dual sweet spot interval, which enhances the interlayer propagation and increased stimulated reservoir volume by 20%.