页岩纹层与破裂方式实验研究

页岩纹层发育,微观非均质性强,页岩破裂方式受多种因素控制。以川南地区X101井龙马溪组深层页岩为研究对象,利用岩芯、薄片、测井资料、X-射线衍射与CT扫描等手段,结合单轴压缩与常规三轴压缩实验,系统研究了页岩破裂方式与纹层产状、矿物组成的关系。结果表明,主压应力垂直纹层方向的单轴压缩岩样形成张拉劈裂破坏,产生80°左右的垂直缝;三轴压缩实验中,主压应力垂直于纹层的岩样形成剪切破坏,裂缝与纹层以45°～65°高角度斜交,主压应力与纹层45°斜交的岩样以沿纹层面的剪切滑移破坏为主,主压应力平行纹层的岩样产生共轭剪切破坏,两者形成的裂缝与纹层呈10°～45°低角度斜交。对于不同纹层倾角的岩样,杨氏模量均与石英含量呈显著正相关,与黏土矿物呈显著负相关的关系,抗压强度与石英、黏土矿物含量的相关性受不同纹层倾角的影响。硅质纹层发育单层厚度大将增强页岩力学性质。

An Experimental Study on Lamina and Fracture Mode of Shale

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.