Analysis Of High-resolution Sequence Stratigraphy In Middle And Upper 3rd Member Of Shahejie Formation (E₂S₃^M-E₂S₃^U),Gubei Sag

Due to the complex characteristics such as multiple faults,multiple provenances,multiple sedimentary systems and multi-phase in the middle and upper subsections of the third Shahejie Formationthe,in the Gubei sag,it is difficult to finely correlate the sand bodies of reservoir in the southern of Gubei sag and the oil-water relationship is intricacy.Based on the principles of high resolution sequence stratigraphy and sedimentology,this paper uses comprehensive analysis of core,well logging,and high-precision seismic data to systematically carried out syudy of highresolution sequence stratigraphy in the middle and upper subsections of the third Shahejie Formationthe,southern sedimentary microfacies,and correlation of sand bodies.Guided by the principles of high-resolution sequence stratigraphy,comprehensively using core,logging,well logging and high-precision seismic data,the Gubei sag in the middle and upper subsections of the third Shahejie Formationthe are divided into two medium-term baselevel cycles and five short-term base level cycles,in which the short-term base level cycles correspond to sand group units,divide five sand group units,and establish a high-resolution sequence isochronous stratigraphic framework.It is pointed out that the strata go through the three processes of lakebasin filling stage-lake transgressive stage-lake basin filling stage,and the strata is fully developed as a whole.The deposition thickness presents a changing trend of thick in the south and thin in the north and the deposition thickness of the strata near the central low swell area is thinner than that on the two sides.Combining the background of stratigraphic development,the 5 sand group units in the middle and upper subsections of Shahejie Formation in the southern gentle slope belt of Gubei sag were further divided and correlated,and a total of11 subzone were divided,in which the mid-term,short-term and super-short-term base level cycles correspond to the oil groups,sand groups,and subzone of the oil field development unit.Aiming at the study of sedimentary microfacies in the southern key areas,based on core and well logging,identify typical sedimentary facies signs,and use point-line-plane sedimentary microfacies research methods to determine that the middle and upper subsections of Shahejie Formation in the southern study area mainly develop delta front subfacies,which are subdivided into underwater distributary channels and underwater inter-distributary bays,mouth bar and sheet sand and other microfacies.The characteristics of delta progression and regression along the provenance direction,and the lateral migration of the delta in the vertical provenance direction.The underwater distributary channels on the plane mainly extend in the northwest direction and the northeast direction,and the water level changes and sediment source supply in different periods,multi-level bifurcation,distribution characteristics and distribution range change.Based on the above research,a fine correlation study of reservoir sand bodies was carried out in the southern part of the Gubei sag,and the static reservoir units were related to the properties of the dynamic oil-water interface inside,and sand body of subzone correlation model guided by the sequence deposition model was proposed.Summarize the stacking law of sand bodies under the change of the A/S ratio during the base level cycle,so as to guide the understanding of the oilwater distribution law in the reservoir,establish the oil-water correlation model in the southern study area,and solve the difficulty of reservoir correlation and the contradictory relationship between oil and water of development issues.