Dynamic mechanical properties and constitutive model of shale with different bedding under triaxial impact test

Abstract

With the gradual depletion of traditional energy sources such as oil and natural gas. As an unconventional energy that can replace traditional resources, shale gas has attracted the attention of the world energy department. The storage environment of shale gas (oil) is usually accompanied by in-situ stress, and the exploitation of shale gas is actually a dynamic process. Therefore, it is of great significance to study the dynamic mechanical characteristics of shale under in-situ stress. In this paper, the dynamic mechanical parameter and constitutive relationship of shales with different bedding (0°, 30°, 45°, 60°, 90°) was studied by the triaxial SHPB tests with the confining pressure from 0 to 15 MPa. The effects of confining pressure on the mechanical properties of shale with different bedding were discussed from the aspects of the dynamic compressive strength, elastic modulus, failure strain, energy characteristics as well as the dynamic failure mode. The experimental results showed that, the dynamic mechanical properties of shale mainly depended on the interaction of the bedding dip angle and various confining pressures. The failure modes of shale under confining pressure mainly present compression shear failure or only damage crack. In additional, a modified dynamic constitutive model of shales was based on the ZWT viscoelastic constitutive relationship, which simplified the low frequency term and took into account shale material damage characteristics. The modified constitutive model is simple in structure and can predict the strength characteristics of shale under confining pressure in a certain range when the basic mechanical parameters and empirical parameters are known.