Effect of Mineral Grain and Hydrate Layered Distribution Characteristics on the Mechanical Properties of Hydrate-Bearing Sediments

The mechanical characteristics of gas hydrate-bearing sediments (HBS) are important for evaluating reservoir stability. The interbedded formation of HBS is common in target mining reservoirs. Existing studies on the triaxial mechanical properties of HBS are primarily based on homogeneous and isotropic samples. Therefore, the stress-strain law of the target mining reservoirs cannot be predicted accurately. In this study, a series of sediment models with interlayers of coarse and fine mineral grains were established based on the PFC3D code, and the influence of the layered distribution characteristics of sediment particles and hydrates on the macroscopic mechanical behaviour of the reservoir was comprehensively analysed. The triaxial compression simulation results indicate that the peak strength, deformation modulus, and cohesion of the layered HBS are significantly lower than those of the homogeneous model. The deformation modulus of the reservoir is mainly affected by the fine-grained layer without hydrates. When the coarse and fine grains correspond to different mineral components, the two minerals are heterogeneous in terms of their micromechanical parameters, which can further reduce the macroscopic mechanical parameters of the HBS. In addition, the layered distribution of hydrate results in significant anisotropy of the reservoir. This study constitutes a reference regarding the control mechanism of gas hydrate reservoir strength.