Natural gas hydrates in sediment are expected to be developed as a resource of natural gas and have been studied as a possible future energy resource. Gas permeability and water permeability in the methane-hydrate (MH)-bearing sediments are important factors for estimating the efficiency of producing methane gas from the natural gas hydrate sediment. Permeability of MH-bearing sediment is considerably affected by several properties of sediment, i.e., pore-size distribution, porosity, cementing, MH saturation, and MH-bearing features. There is no “universal” equation of permeability related with these properties that is applicable to all porous media including MH-bearing sediment. In order to clarify the relation between permeability and these properties, permeability, grain-size distribution, porosity, pore-size distribution, and specific surface area of glass beads and sandy sediments have been measured. The grain-size distribution has been measured by a dynamic laser light scattering-diffraction system. Mercury porosimetry has been used to measure porosity, pore-size distribution, and specific surface area. Proton nuclear magnetic resonance measurement combined with a permeability measurement system was used to characterize the porosity, pore-size distribution and the permeability. The permeability was measured by water.
As a reference, four empirical equations of permeability, i.e., the Krumbeim and Monk equation, the Kozeny-Carman equation, an approximated equation using mercury porosimetry data, and the Schlumberger Doll Research equation, which incorporate factors such as grain size, porosity, pore size, and specific surface area, were scrutinized for calculating permeability.
A semi-empirical (SE) equation of the permeability of glass beads and sandy sediment has been derived based on the Kozeny-Carman equation by pore-size distribution and porosity that had been measured by mercury porosimetry. This SE equation has been approximated by the relation of porosity, pore-size distribution, tortuosity, and specific surface area of the sediment.
The permeabilities calculated by the SE equation correspond well to the permeability measured by water flow.
