Mechanical properties and strain field evolution of organic-rich shale with variable angle shear at real-time high-temperature

In situ mining organic-rich shale by heat injection is a complex solid fluid thermochemical coupling process. The stope and wellbore are subjected to shear stress during the orebody pyrolysis. However, the mechanical response of shale after temperature action is completely different from that under real-time high temperature action. In order to study the shear mechanical properties and deformation evolution law of shale under real-time high temperature, a real-time high-temperature rock variable angle shear test system is designed. By combining acoustic emission and digital image correlation technology, the shear strength and deformation field distribution characteristics of shale under different temperatures and shear angles are thoroughly investigated. The results show that: (1) With the increase of temperature, shale shows a transformation from brittle failure to ductile failure, and the shear strength decreases as the shear angle increases. (2) The shear strength of shale changes in a "V" shape with the increase of temperature. The shear strength of shale decreases to the lowest (2.93 MPa) at 400 degrees C, which can be regarded as the threshold temperature of shale shear properties. When the temperature exceeds 400 degrees C, the shear strength of shale continues to increase due to the transformation of mineral lattice inside. (3) The evolution of the strain field of shale in the shear process at room temperature -600 degrees C can be divided into two stages. At room temperature-400 degrees C, the shale will form an obvious strain localization zone along the bedding structure during shear failure and undergo direct shear failure along the localization zone. In the range of 400-600 degrees C, the shale shows obvious strain softening characteristics, and mutual "stagger shear" occurs along the bedding, instead of shear failure directly along the bedding structure, it shows progressive shear failure characteristics.