Mechanical Creep Instability of Nanocrystalline Methane Hydrates

TL;DR

This study uses molecular dynamics simulations to explore the creep behavior of nanocrystalline methane hydrates, revealing microstructural influences, steady-state creep, and structural transformations that inform their mechanical stability.

Contribution

It provides the first detailed molecular-scale understanding of creep mechanisms in nanocrystalline methane hydrates, including a modified creep model and microstructural insights.

Findings

Long steady-state creep observed in nanocrystalline methane hydrates

Microstructural factors like grain size and boundary diffusion govern creep behavior

Structural transformations significantly influence creep mechanisms

Abstract

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.