Modeling strength characteristics of hydrate-bearing sediments based on discrete element method

It is indispensable for the natural gas hydrate exploration to evaluate the strength and deformation characteristics of hydrate-bearing sediments (HBS) and predict its strength and strain parameters. The main objective of this paper is to model the strength characteristics of HBS based on the discrete element method (DEM) simulation experiments. A preparation method is introduced to fabricate the DEM numerical samples of various HBS. A series of triaxial compression tests are operated on the HBS numerical samples with various conditions. The strength parameters of the HSB with various hydrate saturation and confining pressure, such as failure stresses, failure strains, cohesion and internal friction angles, are determined based on the test results. A strength model, which includes the failure stress evolution equation, the failure strain evolution equation, the cohesive evolution equation and the internal friction angle evolution equation, is developed to represent the strength characteristics of the HSB under various conditions. The cohesion evolution equation describes an exponential relationship between the cohesion and the hydrate saturation. While the internal friction angle evolution equation presents a linear relationship between the internal friction angle and the hydrate saturation. The failure stress evolution equations are based on Mohr-Coulomb criterion and modified Lade-Duncan criterion, respectively. Error analysis shows that the prediction of failure stress based on the modified Lade-Duncan criterion has the higher accuracy. The failure strain evolution equation is based on Mohr-Coulomb criterion, and it has a good performance.