关键词: 层状页岩, 层理面, 破坏模式, 各向异性, 力学特性

Abstract: The anisotropic behavior of layered shale is particularly important during exploring shale gas. To investigate the anisotropic behavior of layered shale of Longmaxi Formation in Shizhu County, the scanning electron microscope tests and uniaxial compression tests are conducted on shale specimens cored at different angles to the shale bedding. The results of microscopic features and uniaxial compressive parameters indicate that the shale is distinctly anisotropic. The stress-strain curve belongs to type II and its five phases are not clearly identified. Under the uniaxial compression condition, there are three types of failure mode: vertical splitting tensile damage with the coring angle of 0°－15°, shear sliding damage along the beddings with the coring angle of 30°－60°, and shear failure across the beddings with the coring angle of 75°－90°. Therefore, the curves are significantly different when the coring angles are variable. It is found that the uniaxial compressive strength (UCS) is minimum when the coring angle is 30°to the shale bedding; the value of UCS is substantially high when the coring angle is around 0°or 90°. The elastic modulus is in good agreement with longitudinal wave velocity, and moreover, both of them decrease with the increase of the coring angle. Since it is difficult to identify the transverse anisotropy of cored samples parallel to the bedding plane, the layered shale of Longmaxi Formation is considered as a transverse isotropic body. The micro fracture and the unique destruction type mainly contributes to the anisotropic properties of the layered shale.

Key words: layered shale, bedding plane, failure mode, anisotropic properties, mechanical characteristics