Investigation of Influence Factors of the Fracture Toughness of Shale: A Case Study of the Longmaxi Formation Shale in Sichuan Basin, China

Abstract

Based on the cracked chevron notched Brazilian disc method, the I-type fracture toughness of Longmaxi Formation shale is measured and the influence of different factors on the fracture toughness of the shales are also discussed. The results show that the fracture toughness of the cores drilled parallel to the bedding ranges from 0.4744 to 0.8752 MPa m0.5 and that of the cores drilled perpendicular to the bedding ranges from 0.4259 to 0.6159 MPa m0.5, which means that the fracture toughness of shale is significantly anisotropy. The clay minerals in the shales have a positive effect on shale fracture toughness while the brittle minerals in shale play a negative role on shale fracture toughness. Being through high temperature processes, the microstructures of the shales are damaged, resulting in lower fracture toughness. Due to the hydration of shales, the interaction between the shale and the water leads to the decrease in the fracture toughness. The increase in the immersion pressure also cause the fracture toughness to decrease.