DISCUSSION ON GAS ORIGINS AND MAIN CONTROLLING FACTORS FOR GAS HYDRATES IN THE SEA OF JAPAN

In order to understand the gas origins and controlling factors for the gas hydrate in the Sea of Japan, data from both the Ulleung and Joetsu Basins are collected and studied. It is found that methane plumes, pockmarks, authigenic carbonates, gas chimneys, BSR and massive hydrate outcrops are quite popular in the Joetsu Basin of northeast Japan Islands, indicating a thermogenic gas origin. However, in the Ulleung Basin, methane plumes are rare, but rich in authigenic carbonates and gas chimneys, and the gas hydrates encountered so far by drilling wells are biogenic. Integrated with the tectonic evolution of the Sea of Japan, it is concluded that thermogenic gas hydrates occurred on the eastern margin of the sea of Japan are mainly controlled by the interaction of the near S—N faults and the near E—W faults, and the later tectonic compression derived by the activity of the faults in NNE—SSW direction. The biogenic gas hydrates with a few thermogenic gas hydrates on the southwestern margin of the Sea of Japan are mainly controlled by the late tectonic compression with a direction of NEE—SWW. Biogenic gas hydrates may dominate the northwestern margin since it was formed earlier and lack of late tectonic compression.