Experimental and Simulation Study for the Dissociation Behavior of Gas Hydrates─Part II: sII Mixed Gas Hydrates

Abstract

This study is an extension of our research on the dissociation behavior of sI CH 4 hydrates (Part I). In this study, investigations of the dissociation of binary and multicomponent structure II hydrates were carried out. A novel approach involving in situ and ex situ Raman spectroscopic measurements together with molecular dynamics simulations were applied for a systematic assessment of the hydrate dissociation and gas release behavior due to the destabilization of hydrate cavities. The hydrate decomposition was induced by thermal stimulation to mimic the warming of oceans and atmosphere brought by climate changes. The interactions between the released gas, aqueous phase, and hydrates were described. The results demonstrated that in the vicinity of the hydrate surface, the liquid phase was oversaturated with the gas molecules and some unstable partial hydrate cavities were also formed. Consequently, the release of gas was temporarily stopped or very slow. Throughout the process, the hydrate underwent decomposition−reformation−continuing decomposition until the crystal disappeared. A faster breakdown of small cavities (5 12 ) was recorded, leading to an increase in the large-to-small cavity ratio during dissociation. Moreover, the results indicated a faster release of CH 4 molecules compared to C 3 H 8 over the dissociation process of the sII CH 4 −C 3 H 8 hydrate. This could be due to the higher diffusivity of CH 4 molecules from the hydrate surface to the gas phase as well as its lower potential to stabilize the cavities compared to C 3 H 8 . The release of CH 4 molecules was also faster compared to CO 2 and C 2 H 6 molecules in the sII mixed hydrate, leading to changes in the hydrate composition throughout the process.

Experimental and Simulation Study for the Dissociation Behavior of Gas Hydrates – Part I: CH4 Hydrates

“…Figure depicts the p-T conditions for laboratory experiments. Raman spectroscopic data are available through GFZ Data Services …”

Prospect and Challenges of Hydrate-Based Hydrogen Storage in the Low-Carbon Future

“…In addition to gas storage, − gas hydrates are relevant to other sectors of the environmental and energy industry such as a cleaner energy source, ,− gas separation and carbon capture, ,− carbon sequestration, − desalination of saline water, − and cold energy storage . Gas hydrates also present a long-standing hazard to the flow assurance in oil and gas industry as they tend to cause flow blockage. − Owing to such scientific and application significances, research in gas hydrates has grown strongly over recent decades.…”