琼东南盆地上新统莺歌海组陆架边缘迁移轨迹及其对深水油气勘探的启示

基于琼东南盆地陆架边缘高精度二维地震资料，利用典型的上超、局部削截、下超及顶超和大型水道下切等地震接触关系，在上新统莺歌海组识别了6套三级层序（自下而上命名为YGH-SQ1、YGH-SQ2、YGH-SQ3、YGH-SQ4、YGH-SQ5和YGH-SQ6）。利用陆架边缘轨迹定量化表征方法，将琼东南盆地上新统莺歌海组邻近陆坡的陆架边缘轨迹划分为负角度下降型、低角度平缓上升型和高角度上升型。上新统莺歌海组6套三级层序发育时期东西两侧的陆架边缘轨迹的演化差异性明显。西部均以下降型或平缓型陆架边缘轨迹为特征；东部以上升型陆架边缘轨迹（YGH-SQ1、YGH-SQ3和YGH-SQ5）为主，在YGH-SQ2和YGH-SQ6时期发育平缓型陆架边缘轨迹，YGH-SQ4时期对应负角度下降型陆架边缘轨迹。侧向上西部陆架边缘进积距离远远大于东部，形成了“西宽东窄”的陆架坡折地貌。综合研究认为，研究区陆架边缘轨迹的垂向迁移由气候变化所引起的海平面升降以及物源供给增强共同控制；而陆架边缘轨迹侧向迁移则主要由构造活动与物源供给的差异性控制。研究区西部物源供给远大于东部且断裂带活动性小于东部，导致西部发育低角度—负角度平缓型陆架迁移轨迹，东部陆坡对应高角度上升型陆架迁移轨迹；负角度下降型和低角度缓慢上升型陆架边缘轨迹则对应陆坡区及深海平原区广泛发育的深水扇，是深水油气富集的有利勘探区。

PLIOCENE SHELF MARGIN MIGRATION TRAJECTORIES IN THE QIONGDONGNAN BASIN AND ITS IMPLICATIONS FOR DEEP WATER HYDROCARBON EXPLORATION

Based on the high-precision 2D seismic data from the shelf margin of the Qiongdongnan Basin, six sequences, namely YGH-SQ1, YGH-SQ2, YGH-SQ3, YGH-SQ4, YGH-SQ5, and YGH-SQ6 from the bottom up are identified for the Pliocene Yinggehai Formation according to the typical seismic contact relationships such as local truncation, onlap, toplap, downlap and incised valley. The quantitative characterization method is adopted to follow up the trajectories of shelf edge. The Pliocene trajectories of the shelf edge of the Yinggehai Period in the Qiodngdongnan Basin can be classified into three types: negative-angle descending, low-angle gently ascending and high-angle ascending, and the vertical evolution of the Pliocene shelf edge track can be divided into six stages, with the descending and gently ascending shelf edge trajectories dominated the west and the gently ascending and ascending shelf edge trajectories dominated the east. In lateral direction the progradation is much larger in the west than that in the east, and thus the shelf slope folds formed in a pattern of “wide in the west and narrow in the east”. Based on the quantitative statistical analysis and previous work, it is clear that the vertical migration of the shelf edge tracks in the study area is mainly controlled by sea level fluctuation caused by climate change and the increase in sediment supply; while the lateral migration of the shelf edge trajectories is mainly controlled by the difference in tectonic activity and sediment supply. The sediment supply in the western part of the study area is much larger than that in the eastern part as the activity of the fracture zone is weaker than that in the eastern part, which leads to the development of the western land slope in the study area. The western part of the study area is much more abundant in sediment supply than that of the eastern part and the fault zone is less active than the eastern part, resulting in the development of the western land slope and the eastern land slope. The land slope areas and deep water fans in the deep-sea plain area are favorable exploration areas for oil and gas, which correspond to the trajectories of the negative-angle descending and low-angle slowly rising shelf edges.