(632h) Effects of Interfacial Properties on the Nucleation Probability and Nucleation Induction Time of Gas Hydrates in Sediments

The formation of gas hydrates is a stochastic process that mainly consists of three stages before reaching equilibrium conditions: saturation, induction, and growth. The first stage is the dissociation of gas molecules in the liquid until the liquid is completely saturated with gas. The second stage is the induction stage, in which small hydrate nuclei form or randomly dissociate until a critical cluster radius is reached. This stage is also known as nucleation stage and is critical for hydrate formation. Once the time necessary to form nuclei of critical radius has been reached, the growth stage begins.

Heterogeneous nucleation takes place during the formation of gas-hydrates in sediments. Unfortunately, there is no clear understanding on the effects of the various interface properties of sediments (i.e., surface wettability, interface curvature and interfacial energies) on the nucleation process of gas hydrates in porous media. Furthermore, it is very difficult to study this problem with experimental methods.

We will present a macroscopic mathematical model incorporating the interface properties that captures the effects of various interfaces on hydrate nucleation. Application of the model allowed for the exploration of how properties like wettability, interface curvature and interfacial energies affect induction time and probability of hydrate nucleation. Model predictions suggest that longer induction time is required to form the same volume of hydrate crystal on gas/liquid/solid triple boundary lines than that on gas/liquid interface. That is, nucleation of methane hydrates preferentially occurs in large sediment pores rather than in small sediment pores. Furthermore, the preference in terms of formation of methane hydrates on different interfaces changes with the volume of the formed hydrate crystal and the curvature of the solid surfaces for any given driving force. Modeling predictions show that gas hydrates form first on the gas/liquid interface, then on the gas/liquid/solid triple boundary lines and last on liquid/solid interfaces.