Effects of hydrate distribution heterogeneity on the mechanical properties of hydrate-bearing sediments with consideration of the coalescence phenomenon: Insights from DEM simulations

Abstract

The heterogeneous distribution of hydrates in natural or synthetic hydrate-bearing sediments (HBSs) has definitively proven its influences on hydrate dissociation and related mechanical responses, which can alter hydrate production strategies. However, due to the limitations of experimental conditions, applicable hydrate heterogeneity characterization and corresponding evaluation of the mechanical properties of HBSs remain lacking. In this study, discrete element modelling of numerical HBSs with different hydrate heterogeneous distributions considering the coalescence phenomenon is performed. The hydrate heterogeneity degree is quantified through image recognition, and the constructed HBSs are subjected to biaxial compression tests. The results show that for two HBSs with the same hydrate saturation above 10 % but highly different hydrate heterogeneity degrees exceeding 0.1, the peak strength, secant modulus and maximum dilation angle of the strongly heterogenous HBSs are lower than those of the weakly heterogenous HBSs. In addition, the weakly heterogeneous HBSs exhibit a more uniform contact force chain structure, more hydrates participate in loading support, and more particle rearrangements, which are the meso-mechanisms for the above macro-mechanical behaviors. Combined with the consideration of the hydrate morphology and cementing ratio, the mechanical properties of HBSs fluctuate due to the randomness of hydrate coalescence but generally show a decreasing trend with increasing hydrate heterogeneity degree. These findings provide an important supplement for understanding the macro- and meso-mechanical properties of HBSs with different hydrate heterogeneity degrees, which indicates that we should precisely describe hydrate coalescence in laboratory experiments and numerical simulations and consider its representativeness in field applications.