Gas permeability characteristics of marine sediments with and without methane hydrates in a core holder

Abstract

Marine methane hydrates have attracted global attentions as a considerable energy resource. The permeability of hydrate reservoirs critically affects the technical and economic feasibility of hydrate exploitation as well as the efficiency of gas production. In this study, marine sediments obtained from the South China Sea were used to remold core samples. Using a core holder, the gas permeability of marine sediments with and without methane hydrates were measured by injecting methane. In this study, the values of gas permeability range from 5.2 mD to 16.7 mD. The effects of confining pressure, hydrate saturation, and initial water saturation on gas permeability of cores were analyzed. The experimental results indicated that the gas permeability decreases (increases) with increasing (decreasing) confining pressure. In addition, the increase trend of confining pressure will significantly decrease on gas permeability in case the effective stress surpassed approximately 3.5 MPa. The deformation of silty-type marine sediments caused by increased confining pressure is irreversible to a certain extent. Relatively, the initial water saturation has little effect on gas permeability. This is attributed to that the water is bounded in the marine soil when the initial water saturation is less than 60%, resulting in a small water resistance effect. In addition, the hydrate dissociation induced by depressurization under confining pressure could result in a decrease of gas permeability. The results of this work revealed the effects of methane hydrates and confining pressure on the gas permeability of marine sediments, with great significance for the methane production from marine methane hydrate reservoirs.