Analysis Of Sequence Stratigraphic Division And Sequence's Control On Reservoirs Of Shahejie Formation In BZ34-2/4 Oilfileld,Huanghekou Sag

Bozhong 34-2/4 oil field is located in the central uplift belt of the Huanghekou depression.The tectonics of this area are complex.Since been put into production,there had been much controversy in stratigraphic division and fine correlation of Shahejie formation,which may stunt the development of the oilfield.Based on the method of seismic stratigraphy and high resolution sequence stratigraphy,combined with seismic,drilling,logging well and core observation,this paper comprehensively focused on the establishment of the isochronal stratigraphic framework,and the analysis of the characteristics of the sedimentary system and the favorable sandbody reservoirs in the isochronous stratigraphic framework.The oil-bearing characteristic are also analyzed,as well as the control of the sequence on the favorable reservoirs.These may contribute into understanding of the distribution of sandbody in the studied area.According to the research ideas of point-line-surface,four three-grade sequence boundaries and five kinds of mid-term datum plane cycles can be identified in the sequence stratigraphic framework under the limitation of combination of well and seismic.The section was divided into three long-term base-level cycles and eight medium-term base cycle.The sequence stratigraphy was in general spreading nearly thick in north and thin in south in E2S3 m,and spreading relatively stable in E3S12.And the sequence stratigraphy's filled characteristics were different in different periods.Braided river delta and lacustrine facies are major sedimentary systems developed in the studied area,which can be further identified as three types of subfacies called braided river delta plain,braided river delta front and shallow lake.In the SQ1,the inputs of detrital from northeastern areas dominated in the studied area,and the braided river delta plain developed well;In the SQ2,it turned to be that the braided river delta front was widely distributed;Then affected by the tectonism,there was a great transition in depositional paleotopography and provenance system in the late SQ2.Thus,the southeast provenance dominated in the SQ3.After comprehensive analysis of lithology,physical properties and oil-bearing possibility,the reservoirs of Shahejie formation in this studied area were divided into three types.On the basis of the analysis above,the vertical and horizontal distribution characteristics of different types of reservoirs in the sequence stratigraphic framework indicate that the favorable reservoir sand bodies are mainly distributed in the vicinity of the three level sequence boundary,the middle and lower part of the base-level rising cycle and the upper part of the base-level declining cycle.