冲绳海槽天然气水合物与地质构造的关系

RELATION BETWEEN GAS HYDRATE AND GEOLOGIC STRUCTURES IN THE OKINAWA TROUGH

海底天然气水合物大多与通过切穿沉积盖层的断裂的上升烃类流体相关,这些高渗透带包括底辟和泥火山等侵入构造,所以海底断裂、底辟和泥火山等构造周围可能赋存天然气水合物;其次,高沉积速率和巨厚沉积层可使有机质迅速掩埋而保存起来,为天然气水合物的生成提供充足物源,因此,邻近陆坡河谷口的海底沉积扇也是天然气水合物赋存的有利地区;另外,由于陆坡区的水合物沉积层比海盆更容易受外界温压变化的影响发生失稳分解,诱发海底滑坡,所以滑坡与天然气水合物赋存之间的关系也非常密切。冲绳海槽邻近海域具有覆水深、沉积厚度大、沉积速率高和有机质丰富等有利赋存条件,目前的研究已经在该海域发现了天然气水合物赋存的地球物理证据BSR,因此,在现有研究基础上开展断裂、泥火山、海底扇、海底滑坡等与天然气水合物相关的构造研究,可以深入了解天然气水合物在不同地质构造中的分布特征与演化,为更精确地评估其资源潜力提供参考。

Marine gas hydrate is mostly related to the lifting hydrocarbon flow through the various fractures in the sediment. The intrusion-related structures such as the diapir and the mud volcano are also the high permeable zone of fluid flow. So there are potentially distributed marine gas hydrate around the fault fracture, the diapir and the mud volcano. On the other hand, the high sedimentation rate and large thickness of sedimentary layer are advantageous to the rapid preservation of organic matter,and provide sufficient hydrocarbon for the forming of the gas hydrate. Therefore the submarine fan near the mouth of the slope valley is the favorable area for the occurrence of gas hydrate. Furthermore, the gas hydrate distributed in the continent slope is more easily influenced by temperature and pressure and more easily suffer from destabilization and decomposition. The decomposition of gas hydrate will induce submarine landslide. So the submarine landslide is also related to the occurrence of gas hydrate. The Okinawa Trough has favorable conditions for gas hydrate such as large water depth,large sediment thickness,high sedimentation rate,and high organic matter. The present study also lets us find geophysical identification sign (BSR) of gas hydrate. So based on the present study results, we should do the relationship study between the gas hydrate occurrence and the fault fracture,mud volcano,submarine fan,and submarine landslide. This study will help to find out the distribution characteristics and the evolution of gas hydrate in the various structural fields, and make a contribution to the resource assessment of gas hydrate.