Study On Sequence Stratigraphy Of The Kongdian Formation In Kongnan Area, Huanghua Depression

Kongnan area is the second oil-rich sag of Huanghua Depression, from Kongdian bulge to Dengming temple. The kongdian formation of palaeogene in kongnan area is the major exploratory target strata of Huanghua Depression. With the study of kongdian formation in kongnan area of huanghua depression, and the directors of sedimentology and sequence stratigraphy, the sequence stratigraphy characteristics of the all sedimentary cycle of kongdian formation were discussed, and the sequence stratigraphic framework and the sequence stratigraphic models were established. It provides scientific basis for the distribution and evolution of sedimentary systems and the exploration of hidden reservoirs in kongnan area.The paper sufficiently considered the regional structural background in kongnan area, utilized existing various datas to carry on seismic facies-electrofacies-lithologic facies trinomial coalition-analysis. Firstly, based on the basic geological and geophysical datas, we proceed seismic interpretation, logging interpretation, core observation and sample test, single-well sedimentological analysis. Secondly, we carry on sequence stratigraphy division: identify the main sequence (system tract) interface, divide the sequence (system tract). Thirdly, we proceed sequence stratigraphy analysis: seismic facies analysis on seismic profiles, high resolution sequence stratigraphy analysis of single-well and sequence contrastive analysis of associated-well profiles. Finally, we establish sequence stratigraphic framework which based on the third-order sequence and sequence stratigraphic models of the region.Through these analysis, we summed up some important recognitions as follows:(1) The basin of kongdian age in kongnan area is the initial rifting stage during the Cenozoic basin evolutive stages of Huanghua Depression, but also a independent basin formation phase, which attributed to rifted-basin. The evolution of the basin can be divided into four stages: intial rifting stage, depressing stage, rifting stage and rifting-filling stage, which corresponding to the four third-order sequences.(2) Kongdian formation of palaeogene in kongnan area can be divided into one second-order sequence (Ek), and four third-order sequences (Ek3, Ek2, Ek1下, Ek1上).(3) According to the different sedimentary feature of each basin edge (eastern, western, southern, northern) in kongnan area, we establish sequence stratigraphic framework and chronostratigraphic framework which based on the third-order sequences of the region, revealing bed succession, systems tract composition, hiatuses feature, temporal and spatial distribution feature of each sequence.(4) We have summed up two sequence stratigraphic models in kongnan area: the northern and the southern parts of the lake basin were mild-slope sequence type, the eastern and the western parts of the lake basin were steep-slope sequence type.