(690f) Modeling the Effects of Interfaces on the Nucleation of Gas Hydrates and Ice in Porous Media

Gas hydrates are water crystalline structures stabilized by the presence of gas molecules. Gas hydrates occur naturally in the permafrost or in ocean-floor sediments at low temperatures and high pressures. Predictions on the amount of methane trapped within gas hydrates contained in marine sediments amounts to three orders of magnitude the worldwide conventional natural-gas reserves. Gas hydrates are an untapped energy resource and a potential contributor to global warming. Mathematical modeling of the stability, formation and dissociation of gas hydrates within sediments is a necessary tool for their management. Due to their similarity to ice, aspects of the behavior of gas hydrates can be modeled similarly to the treatment of ice.

Heterogeneous nucleation takes place during the formation of gas-hydrates and ice in porous media. The presence of surfaces and interfaces within porous media can effectively lower the energy barrier for nucleation. The present work will introduce mathematical models developed in order to describe the effects on energy barriers during heterogeneous nucleation of ice or gas hydrates in porous media. Three different types of interfaces found in these environments will be discussed: a) gas/liquid interfaces, b) solid surfaces, and c) gas/liquid/solid triple boundary lines.

Model predictions suggest that nucleation is more energetically favorable on solid surfaces than at the gas/liquid interface or triple boundary line. In the case of solid surfaces, nucleation is favored within concave surfaces (e.g., inside porous spaces) and to a lesser extent on convex surfaces (e.g., particulates), while flat surfaces act as the behavioral boundary between these two cases. Additionally, hydrophilicity of solid surfaces enhances the positive effect of these surfaces towards nucleation. In the case of gas/liquid interfaces and triple boundary lines, nucleation and crystal growth occur preferentially within the liquid phase rather on the gas phase, and it is favored when the gas/liquid interfaces are present between slightly hydrophobic surfaces.