渤海湾盆地南堡凹陷新近系馆陶组沉积特征

南堡凹陷位于渤海湾盆地黄骅坳陷北部，新近系馆陶组是该凹陷的重要勘探层段。馆陶组以辫状河沉积为主，中段发育曲流河沉积。其油气勘探的首要问题是优质储集砂体的精确对比及有利盖层分布预测。根据高分辨率层序地层学理论以及录井和测井资料，对馆陶组的层序地层样式、沉积特征和储盖组合进行了分析。研究结果表明，该地层具有两种短期旋回和四个中期旋回。在两种短期旋回中，一种是低可容纳空间的非对称旋回，另一种是高可容纳空间的对称旋回。四个中期旋回中，两个以上升半旋回为主体(MSC1、MSC2)，一个是对称旋回(MSC3)，一个以下降半旋回为主体(MSC4)。短、中期旋回均以非对称旋回为主。该地层的长期基准面具有缓慢上升而后快速下降的特点。从MSC1到MSC4旋回，沉积相呈现出冲积扇-辫状河→辫状河-曲流河→曲流河-辫状河相组合的演化过程。自北向南，各中期旋回的可容纳空间增大，沉积主体由砾质河道渐变为砂质河道。由于受基准面中期旋回格架控制，南堡凹陷馆陶组发育上、中、下三套储盖组合。上部储盖组合，因其储、盖层条件最好，应是馆陶组最重要的油气勘探层系。

SEDIMENTARY CHARACTERISTICS OF THE GUANTAO FORMATION OF NEOGENE IN NANPU SAG OF BOHAI BAY BASIN

The Nanpu Sag is located in the northern Huanghua Depression in the Bohai Bay Basin. The Guantao Formation of Neogene in the Sag is the important petroliferous stratum for oil and gas exploration. The sedimentary facies of the Guantao Formation of Neogene are chiefly braided rivers except that the facies are meandering rivers in the middle segment of the Formation. It is the key problem for oil and gas exploration of the Formation to forecast the distribution of advantageous caprocks and to correlate high quality reservoir sand stones accurately. Based on the principle of high resolution sequence stratigraphy and on the information about lithologic log and well-logs, the authors analyzed the patterns of the sequence stratigraphy, the features of sedimentary facies and the combinations of reservoirs and caprocks of the Guantao Formation. The result indicates that the Guantao Formation has developed two kinds of short-term base-level cycles which are respectively unsymmetrical cycle formed in low accommodation and symmetrical cycle formed in high accommodation, and four medium-term base-level cycles , which are two unsymmetrical cycles being chiefly half cycles of base level elevating (MSC1, MSC2), one symmetrical cycle ( MSC3) and one unsymmetrical cycle being chiefly half cycle of base level descending ( MSC4). And both short-term base-level cycles and medium-term base-level cycles are mainly unsymmetrical ones. During the long-term base-level cycle of the Guantao Formation, the base-level elevated slowly and then descended quickly. From MSC1 to MSC4, the sedimentary system of the Formation has changed first from the combination of alluvial fans and braided rivers to the combination of braided rivers and meandering rivers, then to the combination of meandering rivers and braided rivers. From north to south, while the accommodation of each medium-term base-level cycle becomes gradually large, the principal sedimentary facies have gradually changed from gravel channels to sandy channels. Controlled by the framework of medium-term base-level cycles, the Guantao Formation in Nanpu Sag has developed three sets of combinations of reservoirs and caprocks. The upper combination, of which the reservoir and caprocks are the most advantageous, should be the most important target bed of the Guantao Formation in Nanpu Sag for oil and gas exploration.