Molecular Dynamics Simulation of the Effects of Methane Hydrate Phase Transition on Mechanical Properties of Deep-Sea Methane Hydrate-Bearing Soil

Yanmei Zhang,Yalin Luan,Jianlin Liu,Changda Sun,Guoxun Li,Jian Zhang,Angelo Aloisio

doi:10.1155/2021/3716891

Abstract

In this paper, the methane hydrate phase transition process in deep-sea methane hydrate-bearing soil under heating and compression was simulated by the molecular dynamics method. The evolution of deep-sea methane hydrate-bearing soil’s microstructure, system energy, intermolecular interaction energy, and radial distribution function during heating and compression was investigated. The micromechanism of the influence of the methane hydrate phase transition on the mechanical properties of deep-sea methane hydrate-bearing soil was analyzed. The results demonstrated that the methane hydrate dissociation starts from both sides to the middle and the void spaces between the soil particles had nearly no change during the heating process. For the compression process, the methane hydrate on both sides and the middle dissociated at the same time, and the void spaces became smaller. The methane hydrate phase transition on the effects of mechanical properties of the deep-sea methane hydrate-bearing soil is mainly caused by three aspects. (1) the dissociation of methane hydrate incurs the decrease of methane hydrate saturation. The free water and methane molecules generated cannot migrate in time and thus lead to the increase of excess pore water press and excess pore gas press. (2) The dissipated energy causes the decrease of the effective stress between the soil particles. (3) Due to the methane hydrate decomposition, the free water molecules increase, which reduces the friction of soil particles.

Highlights

Methane hydrates, ice-like substances, are formed in the deep-sea soil with high-pressure and low-temperature conditions especially under the seabed on the continental slopes
(3) Due to the methane hydrate decomposition, the free water molecules increase, which reduces the friction of soil particles
As the temperature increased to 276 K, the methane hydrate began to dissociate (Figure 3(b)). e cage structures, which were located on the upper and lower sides of methane hydrate, began to dissociate at the same time, and a passage was formed by the damaged cage structures (Figures 3(b) and 3(c)). e methane molecules moved outside as bubbles along the passage

Summary

Introduction

Ice-like substances, are formed in the deep-sea soil with high-pressure and low-temperature conditions especially under the seabed on the continental slopes. E exploitation of methane hydrates, which is related to methane hydrates dissociation, can lead to the deterioration of mechanical properties of MHBS [3]. E results indicated that the mechanical properties of MHBS deteriorated after the decomposition of methane hydrates. E results showed that the hydrate dissociation has significant impacts on the mechanical properties of MHBS. The deterioration of mechanical properties of MHBS is mainly caused by the dissociation of the methane hydrate. To overcome the current limitations of sampling and experimentation, molecular dynamic (MD) simulations have been utilized to investigate the growth, nucleation, structure, dissociation, and thermodynamic and mechanical characteristics of methane hydrate. Li et al studied the effects of different thermodynamic parameters, temperatures, pressure, and gas concentrations on methane hydrate dissociation with the MD method [23]. E microscopic mechanism of the deterioration of mechanical properties of MHBS was analyzed

Model and Computational Method

Results and Discussion

Conclusions