Numerical simulation of mesoscopic deformation and failure for glutenite in Triassic Baikouquan Formation, Junggar Basin

The Triassic Baikouquan Formation glutenite in the Junggar Basin of western China is rich in tight oil resources. Due to the presence of gravels with varying composition and strength in the glutenite, the mechanical characteristics of the glutenite are significantly affected by the shape, size, and physical properties of the gravels, which in turn affects the fracture complexity and fracturing reconstruction effectiveness of the glutenite reservoirs. In view of this, a method for generating random irregular polygonal gravels was established based on the reservoir characteristics of Baikouquan Formation, Junggar Basin. A mechanical numerical model of the glutenite was created based on particle discrete element method to study the influence mechanism of typical gravel content and distribu-tion on the meso-mechanical characteristics of glutenite. The results show that low-strength gravels have a weak shielding effect on fracture propagation, with most cracks exhibiting a "penetrating gravel" pattern. In contrast, high-strength gravels exhibit a stronger shielding effect, leading to more "bypass gravel" fracture patterns. With increased confining pressure, the compressive strength of the rock significantly increases, along with peak strain energy and slip energy, both showing a linear increase with strain energy being particularly pronounced. In glutenite reservoirs with different gravel combinations, there is a strong linear relationship between the number of shear microcracks and the confining pressure. The glutenite reservoirs with high confining pressure and high-strength gravels exhibit more obvious plastic and ductile characteristics, along with evident secondary failure phenomena. With the decrease of low-strength gravels or the increase of high-strength gravels, the elastic modulus of the glutenite increases, enhancing its resistance to deformation. However, the influence of confining pressure on the elastic modulus of glutenite is minimal across different gravel combinations. The formation and development of macroscopic failure zones in glutenite are largely controlled by the internal meso-structure and are greatly affected by confining pressure and gravel type (mechanical strength).