A research group from Hokkaido University/Graduate School, Okayama University, and Japan Agency for Marine-Earth Science and Technology has elucidated the generation of methane and hydrogen gas originating from thermal decomposition associated with the subduction of the Philippine Sea plate in the Nankai Trough.
Around the Nankai Trough and Sagami Trough, the world's largest gas hydrate containing mainly microbial methane and the world's largest production water-soluble natural gas field are distributed. Microbial methane is made from hydrogen gas (H2) and carbon dioxide (CO2), and although there is sufficient CO2 in the sedimentary layer, there is little organic matter and H2 cannot be obtained very much, so the reason for this large amount of microbial methane production is unknown. was.
The research group speculates that a large amount of hydrogen gas is generated deep underground. Using the latest data, we analyzed and examined the production of methane and hydrogen gas through thermal decomposition of deposited organic matter deep underground, the movement of hydrogen gas, and microbial methane production.
As a result, near the Kumano Sea off the coast of the Kii Peninsula, the production of methane and hydrogen gas originating from pyrolysis has continued for the past approximately 220 million years, and so far, the production of methane and hydrogen gas has been approximately 1 billion m5,900/km per 3 km of the Nankai Trough (approximately the annual consumption of Japan). 5 times) of methane, and the amount of hydrogen gas produced was estimated to be even higher. In the subduction zone (approximately 2000 km) of the Philippine Sea plate, it has been suggested that enormous amounts of methane and hydrogen gas are being produced, and this is still occurring. The methane and hydrogen production zone overlaps with the earthquake rupture zone of the same plate, and it was predicted that methane and hydrogen gas would be released by earthquakes and contribute to the formation of natural gas resources.
Methane originating from pyrolysis may contribute to active methane outflows and mud volcanoes in the region, or may form deep methane pools. There is also the possibility of storing hydrogen gas. The continuous production of methane and hydrogen in the subduction zone of the Philippine Sea plate has been revealed, and it is hoped that future resource exploration will progress.
Paper information:【Communications Earth & Environment】Thermogenic methane and hydrogen generation in subducted sediments of the Nankai Trough
