メタンハイドレート堆積物の浸透率特性―東部南海トラフ基礎試錐メタンハイドレート堆積物の浸透率評価を目的として―

Abstract

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.Glass beads sediment and sandy sediment with different grain sizes have been measured as fundamental research and for application to natural MH-bearing sediment. Sediment pore-size distribution and porosity have been measured by NMR and mercury porosimeter. In order to obtain pore-size distribution with higher spatial resolution, a technique of numerical conversion of NMR-T2 distribution have been developed.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 SE equation has been applied for converted NMR-T2 distribution of MH-bearing sediment. The permeabilities of methane hydrate bearing sediment calculated by the SE equation correspond well to the permeability measured by water flow.