Experimental investigation on anisotropic characteristics of marine shale in Northwestern Hunan, China

The anisotropic characteristics is obviously performed for the marine shale in Northwestern Hunan, China, it's closely related to the developed bedding existing in shale formation layers. While the investigations of the shales' anisotropic behaviors under the different bedding angles are still lacking on comprehensive understanding in this region. In order to understand shales' anisotropic behaviors considering its bedding angle, in this paper, the mechanical properties and failure modes of the marine shales, as well as shales' fragments fractal behaviors were researched based on the elastic strain energy in the shales' failure process. The results show that, the elastic energy release and storage in the failure process of shale are depended on bedding angles, it decides the shales' failure modes, which including piercing blast failure, penetrating shear-slip failure, sliding failure, sliding-shear failure and tensile failure. The findings also indicate that under the different bedding angles, the correlations between the uniaxial compressive strength (UCS), elastic strain energy, and the elastic modulus can be established. Further, via fractal statistics, the relationship between fractal dimensions of the shales' fragments and elastic strain energy has also been obtained. Finally, a novel evaluation scheme was proposed to define the shale's anisotropy grade based on the elastic strain energy. This investigation is significant for the hydraulic fracturing performing design related with the anisotropy characteristics of the marine shale theory.