Study on the Growth Kinetics and Morphology of Methane Hydrate Film in a Porous Glass Microfluidic Device

Xingxun Li,Cunning Wang,Qi Fan,Qingping Li,Guangjin Chen,Changyu Sun

doi:10.3390/en14206814

Abstract

Natural gas hydrates are widely considered one of the most promising green resources with large reserves. Most natural gas hydrates exist in deep-sea porous sediments. In order to achieve highly efficient exploration of natural gas hydrates, a fundamental understanding of hydrate growth becomes highly significant. Most hydrate film growth studies have been carried out on the surface of fluid droplets in in an open space, but some experimental visual works have been performed in a confined porous space. In this work, the growth behavior of methane hydrate film on pore interior surfaces was directly visualized and studied by using a transparent high-pressure glass microfluidic chip with a porous structure. The lateral growth kinetics of methane hydrate film was directly measured on the glass pore interior surface. The dimensionless parameter (−∆G/(RT)) presented by the Gibbs free energy change was used for the expression of driving force to explain the dependence of methane hydrate film growth kinetics and morphology on the driving force in confined pores. The thickening growth phenomenon of the methane hydrate film in micropores was also visualized. The results confirm that the film thickening growth process is mainly determined by water molecule diffusion in the methane hydrate film in glass-confined pores. The findings obtained in this work could help to develop a solid understanding on the formation and growth mechanisms of methane hydrate film in a confined porous space.

Highlights

A solid understanding of natural gas hydrate formation is significant in the exploration of natural gas hydrates
The methane hydrate crystal simultaneously grew and reached the water–methane interface to induce the lateral growth of a methane hydrate film in the glass pores
The microscopic visual results could support the higher mobility of water molecules diffusing through the porous hydrate phase. These results confirm that the film thickening growth of methane hydrate is mainly dominated by the diffusion of water molecules through the hydrate crystal film in confined pores (Figure 7d,e)

Summary

Introduction

A solid understanding of natural gas hydrate formation is significant in the exploration of natural gas hydrates. Hydrate growth kinetics could determine the exact mechanism of hydrate formation. Since most hydrate guest fluids are insoluble at the water phase, a hydrate film with a porous structure first forms on the guest–water phase interface after hydrate nucleation. The hydrate film laterally grows on the guest–water fluid interface, separating the guest and water fluids. This process is defined as hydrate film lateral growth. The lateral and normal hydrate film growth kinetics could directly control the macroscopic hydrate formation behaviors. The hydrate film morphology could reflect hydrate crystal formation characteristics. Investigations on the growth processes of hydrate film, including hydrate film growth kinetics and morphology, are crucial for applications of hydrate-related technologies

Methods

Results

Conclusion