南海北部莺歌海盆地与琼东南盆地油气成藏条件比较研究

THE COMPARATIVE STUDY OF HYDROCARBON ACCUMULATION CONDITIONS IN YINGGEHAI AND QIONGDONGNAN BASINS,NORTHERN SOUTH CHINA SEA

莺歌海盆地与琼东南盆地位于南海北部大陆边缘西部,两盆地虽仅以①号断层相隔,但其油气成藏特征差异明显:莺歌海盆地以中新统三亚—梅山组和上新统底部莺歌海组海相泥岩为主要烃源岩,而琼东南盆地主要烃源岩为渐新统崖城—陵水组近海含煤岩系;泥底辟活动产生的大量垂向断层、裂缝是莺歌海盆地油气垂向运移的主要通道,而琼东南盆地西区则以侧向输导为主,东区兼有垂向和侧向输导特征;莺歌海盆地中新世晚期泥底辟背斜、披覆背斜、断块等构造圈闭及地层岩性圈闭是油气聚集的主要圈闭类型,琼东南盆地则以古近纪构造圈闭为主、新近纪地层岩性圈闭为辅。认为莺歌海盆地下含气系统具有巨大资源潜力,是未来油气勘探的主要靶区;琼东南盆地的主要勘探领域应放在古近系和能与古近系连通的新近纪岩性—构造复合圈闭上,深水区则是该盆地非常重要的油气勘探新领域。

The Yinggehai and Qiongdongnan basins, locate at northwest of the South China Sea. Although they are cut by No. 1 fault, the hydrocarbon accumulation of them are quite different. The main source rocks in the Yinggehai basin involve Sanya and Meishan formations, whereas the sources consist in Yacheng and Lingshui formations in the Qiongdongnan basin. A lot of faults and fractures, which are formed by the diapirs＇ activity, are the pathway for oil ＆ gas migration in the Yinggehai basin, whereas the migration behavior in the western Qiongdongnan basin is vertical, while it is lateral and vertical in the eastern. Structural traps and lithological-structural traps are the main types in the Yinggehai basin, but the structural traps are the main traps in Paleogene, and the lithological structural traps are subsidiary in the Qiongdongnan basin. Hydrocarbon accumulation conditions are the key： factor for the oil ＆ gas exploration strategy. The resource potential at the lower part of the gas system in the Yinggehai basin is great, and will be the main exploration area. Paleogene structural traps and Neogene lithological structural composition traps should be considered as the promising exploration targets in the Qiongdongnan basin. And the deepwater area is also a new favorable prospect in the Qiongdongnan basin.