10:45 〜 12:15
[MIS18-P06] Geological constraints on the heterogeneous crystal structure of gas hydrates from the Umitaka Spur, eastern margin of the Japan Sea
キーワード：ガスハイドレート、結晶構造、日本海、X線回折分析
The Umitaka Spur on the eastern margin of the Japan Sea is characterized by numerous gas chimney structures just below the seafloor where hydrocarbon gas is sufficiently supplied from deep sediments. Gas hydrates accumulate within this system and serve as a huge carbon reservoir near the seafloor. The gas composition of the hydrates (methane, ethane, propane, etc.) determines the crystal structure (Structure I; SI and Structure II; SII), which constrains its stability and gas-water ratio. Therefore, the difference in the microscopic crystal structure of gas hydrates is one of the essential factors for assessing the seafloor environments accompanying gas hydrate accumulation. In this study, we investigated the microscopic distribution of gas hydrate in terms of visual observation (colour and morphology) and crystal structure to examine the geological features controlling the distribution and formation process of gas hydrates on the Umitaka Spur.
The low-temperature X-ray diffraction found the co-existence of SI and SII hydrates. These structures generally reflect the colour difference at the same core; a higher SII/SI ratio for yellowish hydrates and a relatively lower SII/SI ratio for transparent/whitish hydrates. The former contained oil and the SII hydrate predominantly formed with oil-associated heavier hydrocarbon gases. These results indicate that the source and path of gas/fluid responsible for the formation of hydrates might have changed, and SI and SII hydrates did not form simultaneously. Further detailed examination of the distribution of SI and SII hydrate crystals will elucidate the developmental history of gas chimneys.
Samples used in this investigation were collected by Meiji University’s Gas Hydrate Research Laboratory under the commission of AIST from 2013-2015 as part of the methane hydrate research project funded by METI (Ministry of Economy, Trade and Industry).
The low-temperature X-ray diffraction found the co-existence of SI and SII hydrates. These structures generally reflect the colour difference at the same core; a higher SII/SI ratio for yellowish hydrates and a relatively lower SII/SI ratio for transparent/whitish hydrates. The former contained oil and the SII hydrate predominantly formed with oil-associated heavier hydrocarbon gases. These results indicate that the source and path of gas/fluid responsible for the formation of hydrates might have changed, and SI and SII hydrates did not form simultaneously. Further detailed examination of the distribution of SI and SII hydrate crystals will elucidate the developmental history of gas chimneys.
Samples used in this investigation were collected by Meiji University’s Gas Hydrate Research Laboratory under the commission of AIST from 2013-2015 as part of the methane hydrate research project funded by METI (Ministry of Economy, Trade and Industry).