Effect of Gravel Content and Confining Pressure on Mechanical Properties of Conglomerate

The conglomerate reservoir of Baikouquan Formation in Mahu Sag, Junggar Basin, China is rich in oil reserves. However, the reservoir has strong heterogeneity caused by gravel, and it is difficult to master its mechanical properties and laws in laboratory experiments, resulting in difficulties in hydraulic fracturing design. In order to analyze the failure law of conglomerate, the discrete element software PFC2D is used to simulate the triaxial compression test of conglomerate, and the mechanical properties as well as deformation and failure characteristics of conglomerate under different gravel contents and confining pressures are analyzed. The results show that the stress-strain curve of conglomerate presents plastic characteristics, and the plasticity is stronger with the increase of confining pressure and gravel content. The elastic modulus of conglomerate, which has little relation with confining pressure, is mainly controlled by gravel content and is proportional to gravel content. The triaxial compressive strength of conglomerate decreases first and then increases with the increase of gravel content. The conglomerate is supported by hybrid foundation before the critical value, and gravel after the critical value, with a critical value of about 55%. The cohesion increases linearly with gravel content, and the internal friction angle decreases linearly with gravel content. In the triaxial compression test, the failure surface presents “X-shaped”, and the failure, characterized as around gravel failure mode, mainly occurs on the cemented surface.