海底沉积物多边形断层及其对天然气水合物赋存的控制  

Polygonal fault in marine sediments and its impact on gas hydrate occurrence

作　　者：马公正 卢海龙 陆敬安[4] 侯贵廷[1] 龚跃华[4] MAGongzheng;LU Hailong;LU Jing'an;HOU Guiting;GONG Yuehua(School of Earth and Space Sciences,Peking University,Beijing 100871,China;Beijing International Center for Gas Hydrate,Peking University,Beijing 100871,China;College of Engineering,Peking University,Beijing 100871,China;Guangzhou Marine Geological Survey,China Geological Survey,Guangzhou 510075,Guangdong,China)

机构地区：[1]北京大学地球与空间科学学院,北京100871 [2]北京天然气水合物国际研究中心,北京100871 [3]北京大学工学院,北京100871 [4]广州海洋地质调查局,广东广州510075

出　　处：《中国地质》2020年第1期1-13,共13页Geology in China

基　　金：中国地质调查局项目(DD20190234);国家重点研发计划(2017YFC0307603)联合资助~~

摘　　要：多边形断层是一种非构造成因的小型层控伸展断层,多发育于细粒沉积物中,数量多且断距小,断层面在平面上呈不规则多边形排布,在剖面上呈倾向相近或相反的伸展断层。多边形断层的形成机制主要包括"密度反转"、"脱水收缩"和"剪切破裂",不同形成机制所主导的断层形态各有特点。"密度反转"的标志是波状地层接触面;"脱水收缩"的特征是犁状断层和生长层序,直接证据是海底沟纹和沉积物样品中的微裂缝;"剪切破裂"的特征是平直状断层和地堑-地垒式断层组合。多边形断层提高了细粒沉积层的渗透率,可作为烃类气、流体垂向运移的通道。脱水收缩形成的犁状断层流体输导性能可能弱于剪切破裂形成的平直状断层。天然气水合物作为浅表层烃类气、流体运移的产物,其赋存区域也可能会受到多边形断层的控制。分布较深的多边形断层可为天然气水合物提供气、流体运移通道,而分布较浅的多边形断层可为天然气水合物提供储集空间。Polygonal faults are non-tectonic small stratabound extensional faults generally developed in the fine-grained sediments with numerous fault planes and small offset.The fault planes are arranged in irregular polygonal shape in plan view,and occur as extensional faults with similar or opposite inclinations in profile view.The geometry of the polygonal faults is considered to be affected by formation mechanisms,such as density inversion,syneresis and shear failure.The prominent indicator of density inversion is the wave-like surface between horizons.The prominent indicators of syneresis are listric fault planes and growth sequences,and the furrows on the seafloor and the micro-fractures in the sediment samples make up the evidence.The occurrence of polygonal faults improves the permeability of fine-grained sediments,which can provide vertical pathways for gas and fluid migration.The conductivity of listric faults induced by syneresis is inferred to be better than that of straight faults.As a product of shallow gas and fluid migration,the occurrence area of gas hydrate is possibly dominated by polygonal faults.Deep polygonal faults provide pathways of gas and fluid migration for gas hydrate,and shallow polygonal faults provide reservoir spaces for gas hydrate.

关 键 词：海底沉积物 多边形断层 形态特征 形成机制 流体输导性能 天然气水合物 油气勘查工程 

分 类 号：P736.21[天文地球—海洋地质] TE122[天文地球—海洋科学]