Abstract: Shale lamina is well developed with strong micro heterogeneity. In order to form industrial gas flow in shale gas reservoir, fracturing must be carried out, and the fracture mode of shale is controlled by many factors. Taking the deep shale of Well X101 of Longmaxi Formation in South Sichuan as the research object, the relationship between shale fracture mode and mineral composition and occurrence of lamina is systematically studied by means of cores, thin section, logging data, X-ray diffraction and CT scanning, combined with uniaxial compression and conventional triaxial compression experiments. The results indicated that the cores with σ₁ perpendicular to the laminar direction of uniaxial compression form tensile splitting failure, which produce a vertical seam of about 80°; in the triaxial compression test, the cores with σ₁ perpendicular to the lamina form shear failure, the seam and the lamina intersecting obliquely at a high angle of 45°~65°; the rocks oblique crossing with the lamina at a 45° angle is mainly destroyed by shear slip along the grain plane. The results show that the rocks with σ₁ parallel lamina form conjugate shear failure, the seam formed by the two intersecting obliquely with the lamina at a low angle of 10°~45°. For rocks with different lamina occurrence, Young's modulus is significantly positively correlated with quartz content and negatively correlated with clay minerals. The correlation between compressive strength and the content of quartz and clay minerals are affected by different lamina dip angles. The development of siliceous lamina and the large thickness of single layer will enhance the mechanical properties of shale.

Key words: Longmaxi Formation, dip angle of lamina, fracture mode, mineral composition, mechanical parameters