Abstract：

The fracture behaviors of type-Ⅰ cracks in shales with different bedding angles have obvious differences, which in turn affect hydraulic fracturing crack propagation. This paper is based on shale bedding properties, and uses the three-point bending half-disk experimental method to investigate the effect of the angle θ between the bedding plane and type-Ⅰ cracks on the fracture toughness and failure mode. The results show that there is a good secondary correlation between the angle θ and the fracture toughness of the sample. Also, the displacement-pressure curve indicates that a different θ will greatly influence the peak pressure, displacement and fracture type during the loading process. Samples with θ of 45° and 60° show ductile fracture in the post-peak pressure drop stage, while the samples at other angles showed brittle fracture. Moreover, the elastic strain energy increases linearly with increasing bedding angles. The difference in failure mode of cracks in different angle specimens is mainly manifested by the tendency to cracks inclined to the bedding plane and then penetrating the bedding plane. Therefore, the investigation of the influence of the angle between the bedding plane and type-Ⅰ cracks on the fracture toughness and failure mode of the shale has certain significance for guiding the selection of technical parameters during the hydraulic fracturing implementation process, which is beneficial to improving the productivity of fracturing and reforming reservoirs.

Key words：type-Ⅰ shale cracks; bedding angle; fracture toughness; fracture strain energy; fracture mode

Received： 2019-07-26

Corresponding Authors： hancao@csu.edu.cn

Cite this article：MA Like, CAO Han, ZHANG Zheng, GAO Qiang, LUO Zhongshan. An experimental investigation of the fracture behaviors of type-I cracks in shales with different bedding angles. Petroleum Science Bulletin, 2019, 04: 347-353.

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