Numerical Investigation of Bedding Plane Parameters of Transversely Isotropic Shale

Determination of the physical properties of shale is receiving more attention as the numbers of shale gas exploration projects are initiated, and as hydraulic fracturing becomes an integral exploitation method. In particular, anisotropy caused by the bedding structure of shale needs specific attention. In this paper, an anisotropic mineral brittleness-based model (AMBBM) is proposed that makes use of the discrete element method (DEM) to study shale properties, such as anisotropy of non-penetrating bedding planes and separating brittle and non-brittle minerals. Micro-parameters of the AMBBM are calibrated using uniaxial compressive strength tests and by studying the parameter gradient of smooth joints (SJ), such that the strength of SJ mainly affects the failure load in Brazilian tests (FLBT). It is found that the ratio of cohesion to tensile strength of SJ mainly affects the number of cracks formed, which further leads to different failure modes. Normal stiffness and shear stiffness of SJ exerts different effects on FLBT and stiffness in the model. However, the percentage of cracks of various minerals is less affected. The degree of anisotropy is affected by the angle range of parallel bond replaced by bedding plane. Based on the results, a new validation method for AMBBM is proposed, given that the numerical results show good agreement with experimental results, such as FLBT, splitting modulus, and failure mode. The model can thus be used to study seepage properties of shale gas exploitation and hydraulic fracturing by DEM.