多边断层研究现状

多边断层在世界50多个沉积盆地中均有发现,它是指平面上走向多方位且相互交叉组合成多边形形态、具有层控特征的伸展断裂系统,主要发育在被动大陆边缘盆地和内克拉通盆地内的细粒沉积物中。这类断层为非构造成因断层,目前占主流地位的成因机制有密度反转、脱水收缩和重力载荷机制;与构造正断层相比,多边断层明显具有层控性、多边性和体积应变等方性等特点。共同的几何学特征有:延伸长度短,多为平直或铲式断层,倾角变化范围为30°～70°(平均为45°),走向随机,断层平面交叉组合呈多边形形态。多边断层对储层砂体形态以及流体、天然气水合物的运移和聚集具有重要的意义。文中综合了自多边断层提出以来的国内外研究资料,概括了多边断层发育的几何学特征和成因机制以及多边断层对流体运移的影响,希望能对中国以后的多边断层研究提供参考。

Research status of polygonal fault systems

Polygonal fault systems have been identified in more than 50 sedimentary basins world-wide; they are defined as an array of layer-bound extensional faults that exhibit a diverse range of fault strikes,partially or fully intersected to form a polygonal pattern in map view; the polygonal faults are widely developed in fine-grained sediments that have typically undergone passive subsidence in passive margin basins and in some intra-cratonic basins. Those faults are always attributed to the non-tectonic origin,and have been attributed to three genetic mechanisms:density inversion,syneresis and gravity loading. Compared with general normal fault,polygonal faults can be distinguished by layer-bounding,polygonal figures and isotropic orientation of volumetric strain. Their common geometric characteristics are that the fault trace lengths are short,that the faults are planar or gently listric,and that the dips typically range from 30° to 70° (average 45°). Fault traces commonly are not orientated preferentially in any azimuth,and cut bedding surfaces in polygonal geometries. They are very favorable for the migration and accumulation of fluid and gas hydrate and for the geometry of reservoir sand body. Based on reviewing the observations that have published at home and abroad,we summarized the geometric characteristics and genetic mechanism of polygonal fault systems as well as their effects on fluid migration in China. We hope this work could offer a reference for the future study of the polygonal fault systems.