Non-Fickian Diffusion and the Accumulation of Methane Bubbles in Deep-Water Sediments

TL;DR

This paper investigates non-Fickian diffusion mechanisms of methane in deep-water sediments, revealing how they influence bubble accumulation and hydrate deposit formation, with implications for understanding methane hydrate stability.

Contribution

It introduces a model accounting for thermodiffusion and gravitational effects in methane diffusion, highlighting their role in bubble accumulation zones.

Findings

Non-Fickian diffusion significantly affects methane transport.

Extensive bubble accumulation zones can form in deep sediments.

Hydrate deposit capacity is limited by diffusion dynamics.

Abstract

In the absence of fractures, methane bubbles in deep-water sediments can be immovably trapped within a porous matrix by surface tension. The dominant mechanism of transfer of gas mass therefore becomes the diffusion of gas molecules through porewater. The accurate description of this process requires non-Fickian diffusion to be accounted for, including both thermodiffusion and gravitational action. We evaluate the diffusive flux of aqueous methane considering non-Fickian diffusion and predict the existence of extensive bubble mass accumulation zones within deep-water sediments. The limitation on the hydrate deposit capacity is revealed; too weak deposits cannot reach the base of the hydrate stability zone and form any bubbly horizon.