Numerical Study on Mechanical Behaviour of Strongly Heterogeneous Reservoir Under Different Confining Pressure

There are a large number of gravels with irregular shape, size and spatial distribution in the glutenite reservoir. Due to the great difference in mechanical strength between gravels and matrix, the rock mechanical characteristics of glutenite are more complex, showing a strong heterogeneity. In this paper, the particle flow code (PFC) method is used to simulate the deformation and failure characteristics of glutenite under different confining pressures from a microscopic perspective. The results show that the deformation and failure process of glutenite are complex, and the generation of macroscopic failure zone is largely controlled by the internal structure and confining pressure. As the confining pressure increases, the number of tensile micro-fractures generally shows a trend of first increasing and then decreasing, reaching its maximum at a confining pressure of 10–20 MPa, while shear micro-fractures continue to increase remarkably. Regardless of gravel strength, with the increase of confining pressure, the peak strain energy and slip energy increase nearly linearly. Compressive strength of glutenite also increases remarkably with the increase of confining pressure. In addition, the triaxial Young’s modulus is significantly greater than the uniaxial Young’s modulus, but there is little difference in the triaxial Young’s modulus under different confining pressures. As the confining pressure increases, the plastic and ductile characteristics of glutenite become more apparent. Under high confining pressure (30 MPa and 40 MPa) conditions, there is a significant difference in the failure characteristics of glutenite with different gravels. The numerical method proposed in this paper can make up for the shortcomings of physical experiments, better reveal the rock mechanical characteristics of glutenite. The numerical results can provide guidance for drilling, completion and fracturing optimization design.