  Mechanical creep behaviors of natural gas hydrates (NGHs) are of importance
for understanding mechanical instability of gas hydrate-bearing sediments on
Earth. Limited by the experimental challenges, intrinsic creep mechanisms of
nanocrystalline methane hydrates remain largely unknown yet at molecular scale.
Herein, using large-scale molecular dynamics (MD) simulations, mechanical creep
behaviors of nanocrystalline methane hydrates are investigated. It is revealed
that mechanical creep responses are greatly dictated by internal
microstructures of crystalline grain size and external conditions of
temperature and static stress. Interestingly, a long steady-state creep is
observed in nanocrystalline methane hydrates, which can be described by a
modified constitutive Bird-Dorn-Mukherjee model. Microstructural analysis show
that deformations of crystalline grains, grain boundary (GB) diffusion and GB
sliding collectively govern the mechanical creep behaviors of nanocrystalline
methane hydrates. Furthermore, structural transformation also appears important
in their mechanical creep mechanisms. This study sheds new insights into
understanding the mechanical creep scenarios of gas hydrates.
