[M-IS18] Gas hydrates in environmental-resource sciences

[MIS18-P01] Distribution of methane seep in the sea area around Hokkaido and consideration of sampling method

*Satoshi Yamashita¹, Yasutaka Inokuchi¹ (1.Kitami Institute of Technology)

Keywords:methane hydrate, methane seep, mesh structure

In the sea area around Hokkaido, shallow methane hydrates have been collected off Abashiri in the Sea of Okhotsk, off Hidaka and Tokachi in the Pacific Ocean. In places where shallow methane hydrates are present, gas bubbles (methane seep) erupting from the seafloor are often observed using a quantitative echo sounder or a multibeem echo sounder. Methane is also a greenhouse gas with 20 times the greenhouse effect of carbon dioxide, and understanding the distribution and amount of methane seep discharge will lead to a better understanding of global environmental changes. In addition, depending on the seeping scale, it also has potential as a resource. Therefore, in this study, we grasped the distribution of seeping gas and roughly estimated the amount of seeping gas in some areas from the results of surveys conducted so far in the sea area around Hokkaido. In addition, we investigated the sampling method of seeping methane gas.
In the study of the sampling method, we considered using a recovery membrane (net) as a method of gas sampling. Advantages of using a mesh structure include the following. 1) A recovery device can be manufactured at low cost. 2) Due to the mesh structure, there is little resistance due to tidal currents, making it easy to install on the seabed. 3) Excess gas can permeate the mesh and leak to the outside. In order to devise such a recovery system, the gas flow rate, mesh angle, and mesh size were varied, and the permeability of the outflow gas was investigated by a simple laboratory experiment. In addition, a model of the prototype recovery device was installed in a large tank with a diameter of 3m and a height of 3m, and the possibility of gas sampling was also investigated.