マリック地域に分布するガスハイドレートの産状と地質(<特集>メタンハイドレート)

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The Mallik 5L-38 gas hydrate production research well was drilled to 1166m early in 2002, and abundant gas-hydrate-bearing cores were successfully retrieved from a variety of sediments. Gas hydrate-dominant layers were identified at depths of 889 to 1108m. Gas-hydrate-bearing strata typically range from 10cm to a few meters in thickness, and gas hydrate saturations in most gas hydrate layers were auite high. Pore-space hydrate is very small in size and fills the intergranular porosity of sandy sediments. The X-ray CT images of gas-hydrate-bearing sediments always show very uniform CT values. Those values in some parts of the sediment samples suggest that the methane hydrate contents range from 23 to 36 vol.% of the sample, which indicate high methane hydrate saturations in the intergranular porosity of the sand samples. Most of the gas hydrates fill the intergranular pore systems of sands, which are derived from channels and crevasse splay/levee deposits. Gas hydrate is less frequently found in siltstones and mudstones from interdistributary bay and overbank deposits. Measurements of water permeability were undertaken, initially keeping the hydrate stable at 10℃ by pressurizing, and then depressurizing gradually. Initial water permeabilities of gas hydrate/ice filled sands range from 1 to 5 millidarcy. Pore-space hydrate was observed to occur primarily in fine- to medium-grained arenite sands. X-ray diffraction and Raman spectroscopy measurements showed that pore-space hydrates contained in sands are mainly Structure I. P-wave velocities of those sands, measured over the interval -20 to 5℃, decrease from 4 to 3km/sec as water ice melted, S-wave velocities decrease from about 2.5km/sec at -20℃ to about 1.5km/sec at 5℃. Measurements of mechanical strength and electrical resistivity were also undertaken.
一般社団法人日本エネルギー学会の論文
2005-02-20

マリック地域に分布するガスハイドレートの産状と地質(<特集>メタンハイドレート)

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