Study On Sequence Stratigraphy And Depositional Systems Of Shahejie Formation In Banqiao-Beidagang Area

Banqiao-Beidagang area is located in the middle of the Huanghua Depression, the Bohai Bay Basin. The studying area is a typical half-graben subsidence structure that characterized by it's faulted in the north and overlapped in the south, and it is adjacent to Cangxian Uplift and Shenqingzhuang Rize respectively in the north and west, near Beidagang buried hill belt in the south and neighboring the center of Banqiao sag in the east. Shahejie Formation was equipped with the basic geological conditions of stratigraphic traps with multi-stage and multi-types of deposit systems from uplifts and rizes on the edge of studying area. The exploration results have indicated that the studying area has entered a stage of stratigraphic reservoir exploration. The analysis of the type, distribution and evolution of depositional systems, the prediction of favorable reservoir on the basis of geophysical techniques, the analysis of control effect of tectonic geomorphology on ancient depositional systems in sequence stratigraphic framework, all of them have theoretical and practical significance for sequence stratigraphy, depositional system and hydrocarbon exploration in a fault basin.With the guide of sequence stratigraphy theory, the analysis of sequence was made in Shehejie Formation of Banqiao-Beidagang area by the comprehenseive application of 3D seismic, drilling, logging, core, paleontological data. Shahejie Formation can be divided into 7 third-grade sequences. On the basis of well-seismic comprehensive calibration of multi-wells, a sequence stratigraphic framework was established with 3D closed interfaces in Shahejie Formation of Banqiao-Beidagang area.The research on sedimentary systems was made through the comprehensive analysis of core, logging and seismic facies characteristics in accordance with the "point-surface-domain" technical idea on the target sequences of SQEslx, SQEslz, SQEs2. The results show that SQEslx, SQEslz and SQEs2 sequences mainly developed fan delta, beach-bar and gravity flow depositional systems in the context of shallow lake-semi-deep lake in Banqiao-North Dagang area, and the depositional source mainly comes from Cangxian Uplift and Beidagang buried hill. Based on the research in sequence stratigraphy and depositional systems, Esl and Es2 sequences depositional models were established.Based on the research in depositional systems, the prediction of petroleum reservoir was carried out based on geophysical techniques. Firstly, the constrained sparse spike inversion method was used to make quantitative prediction of reservoir in the target sequences, which take the system tracks as unit. Secondly, the hydrocarbon of reservoir was predicted according to the seismic frequency attenuation properties, then the distribution of hydrocarbon reservoir can be optimized.The tectonic geomorphology was recovered during the sedimentary stage of target sequences SQEslx, SQEslz, SQEs2, then the analysis of controlling effects of tectonic geomorphology on the depositional systems was taken. The results show that the ancient geomorphic units can be divided into the outside uplifts and rizes, internal low rizes and troughs, and slope breaks. The configuration relationship between sag and outside uplifts or rizes controlled the location of deposit sources, and the breaking grooves or undercut valleys were supply channels of ancient deposit sources. The internal low rize played a role of resisting and isolating the distribution of depositional systems, which was the favorable area for beach-bar deposits. The internal troughs taken control of the distribution of accommodation space, and then controlled the distribution of sediment volume. The studying area developed fault slope break, faulty-step break and flexure break, and different types of slope breaks had different controlling effects on sequences and depositional systems.Finally, on the basis of analysis about the oil source conditions, hydrocarbon accumulation and reservoir forming model, the favorable exploration area has been forecasted by the comprehensive applications of sequence stratigraphic, tectonic geomorphology and the result of depositional systems and reservoir prediction. The conclusion was that the faulted-nose zone in the lower part of east slope of Shenqingzhuang rize, and the south block of B59 near Dazhangtuo fault were the favorable exploration areas.