Fluid-Solid Coupling Mechanism of Shale Hydraulic Fracture Propagation Based on True Triaxial Test and Numerical Analysis

Hydraulic fracture propagation has a great influence on reservoir reconstruction in shale gas exploitation. The study on mechanism of hydraulic fracture propagation is important. Based on the fluid-solid coupling theory, the propagation criterion under hydraulic pressure of shale is deduced in this paper. In combination with large-scale true triaxial experiment and numerical simulation, the law of hydraulic fracture propagation is researched, and the mechanism of hydraulic fracture propagation is obtained. The results show that shale will produce tensile failure and shear failure under the interaction of water pressure and ground stress. Acoustic emission monitoring data show that the initiation of microfracture is related to water pressure. When the fracture occurs, the number of acoustic emission events increases, and the water pressure drops sharply. Tensile failure occurs mainly at the crack tip, while shear failure occurs mainly at the weak structural plane. When bedding is encountered, hydraulic fracture will be diverted and spread along the bedding. If the strength of the cement inside the bedding is high, the hydraulic fracture passes directly through the weak structural plane. In this paper, the mechanism of shale hydraulic fracture propagation is studied, which has a certain theoretical and practical significance for shale gas fracturing effect evaluation and reservoir stimulation.