南海神狐水合物钻探区不同形态流体地震反射特征与水合物产出的关系

Seismic reflectingcharacteristics of fluid and its effect on gas hydrate distribution in the Shenhu Area,South China Sea

天然气水合物的分布在很大程度上受到含气流体运移的影响。南海北部陆坡区,尤其是珠江口盆地的白云凹陷,普遍存在流体渗漏的现象,暗示了水合物赋存的良好前景。神狐海域水合物钻探区内的高分辨率地震资料显示,区域内发育大量流体运移通道,在地震剖面上表现为不同形态的地震反射模糊带,根据其形态特征,可以划分为花冠状和穹顶状两大类模糊反射带。模糊反射带的存在意味着研究区内具有良好的含气流体运移条件,能够为甲烷气体的垂向运移提供通道。神狐海域水合物的钻探结果表明,水合物的分布与模糊反射带的分布范围具有良好的空间匹配关系,其中,花冠状地震反射模糊带侧翼部与中尺度正断层相连,促进了含气流体的侧向运移,顶部与可能的微裂隙相通,气体可向上运移至水合物稳定带,形成了水合物藏;而穹顶状地震反射模糊带顶部则通过疑似流体通道与海底沟通,这种结构极易形成气体逃逸而无法形成水合物。因此,不同形态特征的模糊反射带可能对水合物的分布具有一定的指示意义。

The distribution of gas hydrate is affected greatly by the migration of gas fluid.The leakage of gas fluid is common in the slope of northern South China Sea,especially in the Baiyun Sag in the Pearl River Mouth Basin,which implies good prospect of gas hydrate occurrence.According to high resolution seismic data about the Shenhu Area,large numbers of fuzzy zones with different morphological characteristics were recognized.They were considered to be main channel of free gas and could be classified into two types：corolliform and dome-form.The existence of fuzzy zones implied that there was a good condition for the migration of gas hydrate in this area,which could provide a vertical channel for free gas migration.Drilling results showed that gas hydrate zones were related to special distribution of fuzzy zones.The corolliform fuzzy zones connected with a set of middle size faults,which promoted the free gas moving to the flank area.The top might connect the small crack with which the free gas could move upwards to the gas hydrate stability zone to form gas hydrate.The top of dome-form fuzzy zones might connect to seafloor through the gas fluid crack.This kind structure could cause the free gas escape and therefore could not form the gas hydrate.This classification method could provide a new indicator about gas hydrate distribution.