Influence of bedding orientation on shale damage evolution:A combined in-situ micro-CT and digital volume correlation investigationOA

The bedding structure of shale significantly influences its mechanical anisotropy.However,the meso-scale anisotropic control mechanism of bedding on shale damage evolution remains insufficiently understood.This study employs in-situ uniaxial compression CT scanning experiments,combined with grayscale thresholding and deep learning-based image segmentation,to achieve high-precision 3D reconstructions of shale pore-fracture networks.Additionally,by integrating Digital Volume Correlation(DVC)with image analysis,a cross-scale quantitative characterization and synergistic evaluation are conducted,bridging the evolution of microstructural damage with macroscopic full-field deformation in bedded shale.The results reveal that:(1)The dominant geometric factors influencing the complexity of the shale pore-fracture network during loading vary with bedding orientation:number and spatial distribution dominate for 0°shale,volume and area for 30°/60°shale,and coupled geometric parameters for 90°shale.(2)Displacement and strain fields exhibit distinct characteristics related to the bedding angle:0°shale shows quasi-uniform deformation dominated by axial compaction;30°and 60°shales form significant strain concentration bands along bedding planes due to shear slip effects;90°shale is driven by radial tension,leading to tensile strain localization parallel to the bedding direction.(3)The strain accommodation mechanism in shale transitions with the bedding angle:it shifts from being dominated by matrix compaction and diffuse micro-damage at low angles to being primarily controlled by fracture propagation along bedding planes at high angles.In high-angle bedded shale,pre-existing pores and fractures tend to preferentially act as nucleation sites for damage initiation and strain localization.