Effect of Gas Hydrate Saturation on Hydraulic Conductivity of Marine Sediments

Abstract

Methane gas, one of the unconventional energy sources, is stored under the seabed or permafrost as a form of gas hydrate. Numerous countries are researching gas hydrate production. One of the production methods is depressurization which induces the dissociation of gas hydrates by pumping pore water through the production well. The water pumping reduces the pore pressure lower than the equilibrium pressure of the gas hydrates. Thus, the dissociation rate and gas productivity are significantly dependent on the water permeability (i.e., hydraulic conductivity) in hydrate-bearing sediments. The hydraulic conductivity of hydrate-bearing sediments is considerably affected by gas hydrate saturation because the gas hydrates generally exist as a porefilling and fracture-filling solid in the sediment pores. Therefore, the purpose of this research was to determine the correlation between gas hydrate saturation and hydraulic conductivity in sediments through various laboratory experiments. In the experiment, gas hydrates were synthesized in a high pressure oedometer cell, with an artificial specimen which has a similar grain size distribution with a recovered core sample from the Ulleung basin of Korea. Gas hydrate formation and dissociation were monitored by geophysical sensors including P-and S-wave and electrical resistivity sensors. The experimental results suggest there is an empirical relationship between gas hydrate saturation and water permeability in gas hydrate-bearing sediments.