The Sequence Stratigraphy And Sedimentary Systems Of Member 1～3 Of Shahejie Formation Of The Eogene In Diannan Area Of Jizhong Sag

The Member 1~3 of Shahejie Formation is the major exploration target of Diannan area. As exploration becomes more and more difficult, the exploratory objects transfer gradually from the structure reservoirs which are easy to be distinguished to subtle reservoirs, such as lithologic or stratigraphic reservoirs. So,more accurate research results of sedimentary facies and sandbody distribution are needed urgently. The key target of sequence stratigraphy is just to construct isochronous lithologic and lithofacies framework for the study on facies and depositional systems, then to predict the reservoir distribution and reservoir-cap rock assemblage more efficiently.By the studying of plentiful geological and geophysical data, and based on the fundamental principles of sequence stratigraphy and sedimentology, the isochronal framework of sequence stratigraphy and sedimentary system model of Member 1~3 of Shahejie Formation were established. The depositional system distribution and control factors in isochronal frame of sequence stratigraphy were discussed further; the reservoir characters of various sandbodies, the distribution and control factors of lithologic-stratigraphic traps were analysed too. At last, the directions and new goals of petroleum prospecting were pointed out.Based on the boundary marks of sequence stratigraphies at all levels, all the sequences and their boundaries of the Member 1~3 of Shahejie Formation were delineated. The Palaeogene Formation can be subdivided into three 2nd-order sequences with ten 3rd-order sequences. Through sequence stratigraphic subdivision and correlation of key wells and seismic sections,the sequence stratigraphic framework and sedimentary system models were established; the "weishayan" in Member 1 belonging to lowstand system tract was put forward, and this conclusion is proved by exploration practice.On the integrative analysis on core facies, log facies, and seismic facies etc, the delta, braided delta, lacutrine and tempestite deposits have been identified. They can be subdivided into 6 subfacies, 21 microfacies,and the relevant sedimentary models have been set up. The tempestite is the first discovery in the area, which is significant both in theory and in hydrocarbon reservoir prediction. The sedimentary systems type and its distribution, reservoir-cap rock assemblage, the control factors of sequences, systems tracts and sandbodies distribution have been studied in the isochronal frames of sequence stratigraphy. The sandbody types are controlled by systems tracts, the highstand systems tract and transgressive systems tract are rich in sand, while the lowstand systems tract is poor in sand. The distribution is controlled by the tectonic, palaeotopography, provenance and climate.Acording to the characteristics of sedimentary system distribution and source rock , reservoir-cap rock assemblage, combinated with tectonics styles, hydrocarbon migration, the hydrocarbon occurrence and the model of hydrocarbonate accommodation were summarized. At last, the favorable districts for the subtle reservoirs were pointed out.