琼东南盆地华光凹陷构造特征及沉积充填

STRUCTURAL PATTERN AND SEDIMENT FILLING IN HUAGUANG SAG OF SOUTHERN QIONGDONGNAN BASIN

南海北部大陆边缘发育多个新生代含油气盆地。近年来,在南海北部珠江口盆地南部深水区陆续发现大中型气藏,证实了该区油气地质条件优越。琼东南盆地南部深水区与珠江口盆地深水区具有相似的构造沉积演化史,油气地质条件相似,具有形成大中型油气藏的地质条件,因此十分有必要开展该区的构造特征及沉积充填研究。基于近年来新采集的高精度地震资料,对华光凹陷构造特征进行详细分析,认为区内发育4种伸展构造样式,分别是地堑、半地堑、多米诺式半地堑和地垒;经历两个构造演化阶段,形成"下断上拗"的双层结构特征,相应发育两个期次的正断层。下构造层古近系受裂陷作用控制,断层发育,地层分布受断裂控制明显,上构造层新近系-第四系构造活动微弱,断层不发育,地层变形小且沉积厚度趋于稳定。华光凹陷古近系为河湖相-海陆过渡相沉积,其中下渐新统崖城组煤系地层是琼东南盆地勘探证实的主要烃源岩层系,上渐新统陵水组是主要储层发育时期,新近系-第四系为浅海-半深海-深海相沉积,其中中新统储层发育,上中新统及以上海相泥岩是良好的盖层。因此,华光凹陷具有良好的生储盖组合。

A great number of Cenozoic petroleum basins have been discovered in the northern continental margin of the South China Sea.Two of them,the Qiongdongnan Basin and the Pearl River Mouth Basin are located in the deepwater area of the region.Recently medium and large petroleum discoveries have been obtained in the southern deepwater area of the Pearl River Mouth Basin.It verifies that favorable petroleum geological conditions occur in the deepwater area.Having similar tectonic and depositional evolutionary history with the Pearl River Mouth Basin,the southern deepwater area of the Qiongdongnan Basin should have the same potential to form medium to large gas reservoirs.It,therefore,has become a necessity to study this area in details.The accumulation of high resolution seismic data in recent years has made it possible to understand more about the structural pattern of the deepwater area of the Qiongdongnan Basin.In this regard,the Huaguang Sag was selected as a case for study.Our study reveals that there are four types of extensional structures in the area,namely graben,half graban,terraced garaben and terraced half graben,formed in two stages,corresponding to the two regional structural evaluation stages in the region.There is an obvious double-layer vertical architecture in the sag,including the rifting lower layer and the subsiding upper layer,and four units have been recognized in the sag according to the structural pattern,namely the western sag,eastern sag,middle horst and the southern slope.The distribution of Paleogene deposits or the lower layer is obviously controlled by rifting.The tectonic activities in Neogene or the upper layer were rather weak.There is little tectonic deformation.The double layer architecture has provided an excellent combination for hydrocarbon accumulation.