DEM investigation of the effect of hydrate morphology on the mechanical properties of hydrate-bearing sands

Understanding the engineering properties of hydrate-bearing sands (HBS) is the key to assessing the safety during the exploitation of natural gas hydrates. The formation and presence of hydrates in pore spaces are complicated, yet the HBS specimens with different hydrate morphologies have not been precisely tested due to the difficulty in controlling the hydrate formation in the laboratory. In this study, the discrete element method (DEM) is used to create HBS models containing pore-filling, cementing, load-bearing, grain-coating, and patchy hydrates. A series of HBS specimens with different hydrate morphologies and hydrate saturations ranging from 0 to 40% are tested by simulating biaxial compression tests. The numerical results show that the shear strength is slightly but the secant modulus is significantly influenced by the hydrate morphology. The shear strength and secant modulus of HBS increase with hydrate saturation regardless of the hydrate morphology. Further relationships are established between the micro mechanical analyses of the evolution of bonds and contact-type-related contributions and the macro mechanical properties of HBS. These DEM results can provide lower and upper limits for HBS, which are beneficial for further understanding the mechanical responses of HBS with complex hydrate morphologies.