Brazilian splitting experiment and finite element simulation analysis of the influence of bedding loading angle on shale fracture mode

Abstract

During the diagenetic processes of compaction and cementation, shale forms multiple beddings, significantly effecting the rock anisotropy. Therefore, it is important to study the effect of bedding on the mechanical properties of shale to guide fracturing engineering. To study the failure mode and fracture morphology of shale with bedding planes under different bedding dip angles, Brazilian disc splitting tests and finite element numerical simulations are performed for shale samples and the results are compared. (1) The bedding angle has a significant effect on the failure mode and tensile strength of shale, and the tensile strength tends to increase with increasing bedding angle. (2) The failure modes of shale under different bedding dip angles can be divided into three types: tensile failure along the bedding plane; comprehensive shear and tensile failure of the matrix and the bedding plane; and matrix tensile failure. (3) The direction of secondary cracks is mostly perpendicular to the bedding plane, and a smaller angle between the load application direction and the bedding direction results in a larger number of generated cracks with more complex shapes. (4) When the loading angle of the bedding is 30°, the tensile strength is low and the matrix and the bedding plane are comprehensively destroyed by shear and tension, resulting in a more complex joint mesh; conversely, when the bedding angle is greater than 60°, the tensile strength increases and the complexity of the seam mesh decreases. These findings can provide guidance for the selection of the bedding angle and the design of fracturing schemes in fracturing engineering.