莺歌海盆地与琼东南盆地成藏条件的比较及天然气勘探方向

莺歌海盆地和琼东南盆地常被合称为莺琼盆地，但二者的天然气成藏条件明显不同，莺歌海盆地第三－第四系巨厚，老第三纪崖城组和陵水组强烈过成熟，有效源岩为新第三纪三亚组和梅山组，而琼东南盆地的主要源岩为崖城组和陵水组，上第三系的生烃强度较低；尽管莺歌海盆地和琼东南盆地均为超压盆地，但莺歌海盆地强超压和右旋张扭应力场的共同作用导致超压囊顶部破裂并发育底辟，实现了超压流体包括天然气的垂向集中排放，而琼东南盆地总体上仍为侧向分散流体系统。莺歌海盆地的重要勘探领域是与底辟有关的圈闭，而琼东南盆地的主要勘探领域应为与下第三系源岩具有良好输导通道的上第三系岩性－构造复合圈闭或下第三系构造圈闭。

DIFFERENCE IN NATURAL GAS ACCUMULATION CONDITIONS BETWEEN YINGGEHAI AND QIONGDONGNAN BASINS AND ITS IMPLICATIONS FOR NATURAL GAS EXPLORATION

The Yinggehai and Qiongdongnan basins, often called Ying Qiong basin, are quite different in their petroleum accumulations. The Tertiary and Quaternary sediments in the Yinggehai basin is up to 17 km thick, with the Oligocene Yacheng and Lingshui formations over mature. Therefore, the effective source rocks are the Sanya and Meishan formations. The main source rocks in the Qiongdongnan basin are the Yacheng and Lingshui formations. Although both basins are overpressured, their fluid flows are greatly different. The combination of strong overpressure and tensile stress field caused by the right lateral slipping movement has led both to the fractures in the top layers of the over pressure systems and to the occurrences of diapirs, an expulsion pathway for the overpressured fluids including natural gases. The fluid flow in the Qiongdongnan basin, however, is compaction driven, and laterally dispersed from the deep depression towards its surrounding areas with a relatively low fluid potential. Traps associated with diapirs are regarded as important exploration targets in the Yinggehai basin, whereas the Neogene lithological structural complex traps with the excellent pathways to the Oligocene source rocks or the Oligocene structural traps should be considered as the main exploration targets in the Qiongdongnan basin.