Hydrate is a Nonwetting Phase in Porous Media

In porous media containing gas hydrate, the hydrate morphology impacts the flow behavior of the fluid phases. We hypothesize that hydrate emplaces itself as a nonwetting phase and use this idea to describe relative permeability of water in a hydrate/water system. We perform steady-state relative permeability measurements in hydrate-bearing samples with a range of hydrate saturation. We measure and compare water relative permeability in the presence of gas and in the presence of hydrate and find that the water relative permeability is the same in both cases. This suggests that (1) relative permeability for hydrate systems can be obtained without performing difficult experiments on hydrate bearing sediments, (2) flow properties are porous-media dependent, and (3) models that assume a fixed pore or tube geometry are inadequate. Plain Language Summary Methane hydrates are an ice-like solid composed of water and methane gas. They are found in high pressure and low temperature environments such as deep-sea sediments. Hydrate reservoirs represent a significant portion of the global carbon cycle and are of great interest for energy production, CO2 storage, geohazards, and more. Fluid flow properties of hydrate-bearing sediments control how hydrate forms, dissociates, and evolves. When more than one phase is present in the pore space, the fluids will impede the ability for other fluids to flow and this reduction is parameterized as relative permeability. We propose that hydrate will occupy a fraction of the pore space like a nonwetting fluid phase such as gas or oil. We performed experiments that show water relative permeability is the same for a given porous medium with gas or hydrate. Therefore, the relative permeability for hydrate systems can be understood in the same context as relative permeability for nonhydrate systems and the relative permeability for hydrate systems can be obtained without performing difficult experiments on hydrate bearing sediments.