Abstract:

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.

Key words: polygonal fault, geometry, genetic mechanism, fluid migration pathway