Effects of bedding properties on fracture behavior in shale with 3D bedding planes: Insights from DEM simulation

The mechanical and spatial properties of bedding planes significantly affect shale fracture characteristics. To investigate the influence of bedding properties on the mode I fracture behavior of shale, numerical models with different bedding properties were developed based on experimental results. These models were employed to evaluate the influences of the bedding angle and tensile strength on the apparent fracture toughness (AFT), damage ratio, and crack distribution patterns. The angles α and β represent the horizontal projection angles of the bedding plane in the x and y directions, respectively. The results indicated that an increased tensile strength ratio (TSR) between the bedding and the matrix significantly enhanced the AFT, particularly when the bedding planes were subjected to tensile stress. Moreover, increased TSR values correlated with reduced propagation distances of microcrack in bedding planes, while increased bedding angle β significantly inhibited crack propagation. In addition, a higher TSR could inhibit the formation of secondary cracks in the bedding plane. Notably, there were significant differences in the damage ratio for different bedding angles, with the highest damage ratio observed for mixed failure. When the angles are α = 90°, and β = 30°, the damage ratio remains the highest under different TSRs. The results indicate that setting the fracturing direction relative to the bedding plane at α = 90° and β = 30° can promote mixed shale failure and significantly improve hydraulic fracturing efficiency.