日本海天然气水合物气源成因及主控因素探讨

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

为了探讨日本海天然气水合物的气源成因及其控制因素,收集和整理了日本海西南郁陵盆地和日本海东缘上越盆地及邻近的相关资料。结果显示,上越盆地及邻近海域甲烷羽状流、麻坑、自生碳酸盐岩及地震剖面上"气烟囱"和BSR等发育,块状水合物出露海底为热解成因;郁陵盆地羽状流不太发育,而自生碳酸盐岩和地震剖面上的"气烟囱"较发育,钻孔发现的水合物主要为生物成因。结合日本海构造演化特征综合分析认为,日本海东缘热解成因水合物的主控因素是近S—N向和近E—W向交互断裂作用以及NE—SW向的晚期构造挤压;日本海西南海域生物成因为主兼热解成因水合物的主控因素是NEE—SWW向的晚期构造挤压;而日本海西北海域构造定型早且缺少晚期构造挤压,因此,推测其水合物气源应该主要为生物成因,热成因的可能性很小。

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.