The Study On The Sequence Stratigraphy And Sedimentary System In Paleogen Of Xihu Sag In The East China Sea Shelf Basin

Xihu sag is NNE-extension,which is the deepest sag in the northeast of the East China sea shelf basin. The oil and gas reserves has been proven,controlled and forecast,and the Long-term resources, Show that the encouraging prospects of the Xihu Sag. Therefore which is the main battlefield of exploration of the East China Sea shelf basin. Based on the needs of oil and gas exploration and the significance of Sequence stratigraphy in the prediction of lithological reservoir distribution,the Pinghu formation and Xihu formation were chosen as the main purpose of the objective interval.The contents of this paper are presented as follows:The seismic and logging information is indicaed that there are five unconformity surfaces in Paleogen, Xihu sag. With these unconformity surfaces and the corresponding conformity surfaces, the research area can be divided into five stratigraphic sequences, Sequenceâ… (the fifth member in Pinghu Fm.), Sequenceâ…¡(the third and fourth member in Pinghu Fm.), Sequenceâ…¢(the first and second member in Pinghu Fm.) , Sequenceâ…£(lower of Huagang Fm.),and Sequenceâ…¤(upper of Huagang Fm.).The stratum data of part of Sequenceâ…¢and part of Sequenceâ…£were redrew by applying the INPEFA technology.Classified individual well lithologic sequence and facies about 9 Wells in the region, studied seismic and sedimentary facies, built sedimentary facies and subfacies classification system, which suit the region crop ,of which logging and seismic could be identified.Seven kinds of sedimentary pattern and sixteen are recognized,which are fluvial facies,lake facies,river delta pattern,fan delta pattern,braided delta pattern, tidal delta pattern and tidal-flat facies. And more detailed classifieation of sedimentary subfacies and microfacies for each sedimentary facies are also made in the work. According to the facies have been recognized,profiles of wells-correlation are made to show the stratum comparison.The analysis for sequence stratigraphy in 12 single well is base on the characters of well logging , lithology, drilling core and INPEFA wells. The division of seismic sequence is contributed according to the unconformity surfaces. Based on the resources mentioned above,the paper establish the Paleogen high resolution isochronous sequence stratigraphic framework.In light of the seismic facics classification principle of external geometric shape plus internal reffector configuration, seven seismic facies, including parallel or sub-parallel sheet facies, lens pattern,disorderly filling facies, progradation facies, hummocky facies, and wedge facies, are recognized from the seismic reflection corresponding to Pinghu Formation and Xihu formation which are prospective for oil and gas exploration. Craggedness is mainly wedge clutter pattern, and belong to fan-delta seismic response; gently zone is mainly progradation facies, belong to river or tidal delta seismic response; the central uplift belt corresponds to braided delta,which come from the fan-delta;the rear between the Craggedness and the central uplift belt filled with middle swing pattern and middle-high frequency which reflect shore-shallow lake facies.The Geological interpretation of seismic profiles are made accoring to the relationship between the seismic facies and the sedimentary facies.Considering that the research about the deposional system is the foundation of reservoir evaluation and prediction,Firstly, this thesis probe the direction of minerals source;then,referance the seismic facies and the sedimentary facies material,and according to region sedimentary frame and sedimentary action, this thesis discussing the distribution of depositional systems on different phases.The contribution of this thesis is that sequence boundries between the base level asending and descending are more precise by applying the INPEFA technology.