琼东南盆地北礁凹陷多边形断层发育特征及成因

基于高精度三维地震解释和相干属性分析,发现琼东南盆地北礁凹陷三维区中新统三亚组、梅山组、黄流组发育大量多边形断层。梅山组顶面发育呈近EW向展布的长条形丘和丘间底流水道,其上方分别发育近EW向(多边形)断层密集带和近SN向横截水道(多边形)断层。北部泥岩区,丘规模越大,断层密集带越宽,断层密集带主要分布在黄流组下部和梅山组上段地层中,横截底流水道断层向上延伸较短,向下延伸至梅山组或三亚组,而梅山组至三亚组多边形断层逐渐呈现多边形形态。西南部砂岩区,黄流组底部断层密集带和横截水道断层比北部规模小,延伸短,梅山组下段发育近NE向横截浊积水道砂岩断层和近NW向平行浊积水道边界断层,其规模更小。重力扩展可以很好地解释黄流组断层密集带和横截底流水道断层的形成,梅山组和三亚组的多边形断层是超压水力破裂的结果,同时大颗粒砂岩抑制多边形断层的形成。在我国首次发现断层密集带和横截水道断层,该类断层对油气运移、识别强振幅地质体和丘形反射成因具有重要的意义。

Characteristics and Genesis of the Polygonal Fault System in Beijiao Sag of the Qiongdongnan Basin,the Northern South China Sea

Based on 3D high-resolution seismic interpretation and coherent attribute analysis,the polygonal fault system (PFS) discovered in the Beijiao Sag of the Qiongdongnan (QDN) Basin was discussed in detail.PFS occurred in the study area from the Shanya Formation to the Huangliu Formation.The characteristics of the PFS are diverse in the different areas.The elongated mounds and bottom current channels between mounds at the top of the Meishan Formation were nearly E-W oriented.The (polygonal) fault concentrated belts (FCBs) and traversed-channel (polygonal)faults (TCFs) were developed on the mounds and bottom current channels respectively.In the northern mudstone area,the larger the mound is,the wider the FCB is.The FCBs mainly occur at the bottom of the Huangliu Formation and the upper Meishan Formation.The TCFs extended from the Huangliu Formation to the Meishan Formation or to the Sanya Formation,while the extension of TCFs was limited in the bottom of the Huangliu Formation.However,the PFS gradually presents omni-direction in the Meishan and the Shanya Formations.In the southwestern sandstone area,the scale of FCBs and TCFs in the bottom of the Huangliu Formation is smaller than those in the northern mudstone area.In the lower Meishan Formation the scale of nearly N-E striking TCFs and nearly N-W striking FCBs along the boundary of turbidite channels is much smaller than the others.Gravitational spreading can account for the genesis of the FCBs and TCFs reasonably.Overpressure syneresis resulted mainly in the formation of PFS within the Meishan and Shanya Formations.Meanwhile,the coarse grain sandstone inhibited the formation of PFS.The discovery of FCBs and TCFs has a great significance in tracing hydrocarbon migration,identifying strong amplitude geologic bodies and inferring the genesis of mounded reflection.