Study On Sequence Stratigraphy And Depositional System Of Dongying Formationin,Nanpu Sag

Nanpu Sag is an oil and gas accumulation area in the north of Huanghua depression,Bohai Bay basin.Many oil-bearing strata has been confirmed and it has great exploration potential.In this paper,based on the theory of sedimentology and sequence stratigraphy,the main research contents contain recognition of the sequence stratigraphy interfere and construction of stratigraphic framework,provenance system analysis,and analysis of sedimentary facies and sedimentary system,which provide the scientific basis for searching for sand body and“sweet point”in reservoir.According to the response characteristics of sequence boundary in the core,logging and seismic data,five sequence boundary is identified.It is considered that the Dongying formation in Nanpu Sag is a long-term base level cycle deposition(two order sequence),and can be further divided into 4 3~rdd order sequences,which have a certain corresponding relationship with the traditional geological stratification.Then we establish the isochronous stratigraphic framework in the whole area by the tracking the key sequence interface.We pick the flooding surface by using the well logging data,and the high resolution sequence stratigraphy are divided and compared.According to the analysis of rock debris composition and heavy mineral analysis combined with palaeogomorphic features,it shows that there are two source in Dongying formation:the maturity of the sediments in the north is decreasing from north to south,the Beipu west,Laoyemiao,and Gaoshangbao are the source entrance,and the sediment maturity in the south is decreasing from the south to the north,and the source entrance is the Nanpu 1 structural belt and the Nanpu 2 tectonic belt.Based on the core facies analysis,log facies analysis and seismic facies analysis,the sedimentary systems are composed by four sedimentary facies:the whole sag were continental lacustrine in graben basin,the fan delta facies come from north steep slop,the braided river delta went forward from south gentle slop,the gravity flow deposit at the low part of sdimentary systems.The distribution and evolution of the depositional system are depicted in the stratigraphic frame.