Sedimentary Characteristics Of The Second Member Of The Shahejie Formation In The Ying 17 Fault Block From Dongxin Oilfield

Ying 17 fault block,Dongxin oilfield is located in the middle of Dongying sag,and is a typical complex fault block oil-gas reservoir.The second member of the Shahejie Formation?Es₂?is the main oil layer.Via comprehensively utilizing data of seismic,logging,mud logging and cores,the paper establishes the sequence stratigraphic framework of Es₂ in the Ying 17 fault block,and divides Es₂ into two third-order sequences,Sequence?and Sequence?.The third-order sequence can be subdivided into lowstand systems tract,transgressive systems tract and highstand systems tract.According to the change of lithology and superimposed relationship,it is subdivided into 16 fourth-order sequences,corresponding to 16 sand groups,Es₂¹?Es₂¹⁵?Es₂^W16,and 124 single layers.The main sedimentary facies of Es₂ in the study area are braided river delta sedimentary systems,sedimentary evolution and sand body development are mainly controlled by the Dongying Delta and show regular change.During the Es₂,Dongying Delta is under the background of the water regression,so it presents continuous progradation process from east to west.During Es₂^W,the lake is relatively stable,developing the delta front subfacies;Es₂¹⁵ develops prodelta parfacy;In the period of Es₂¹⁴?Es₂⁸,the lake level shows a continuously stable decline,and develops the delta front subfacies,including mouth bar,underwater distributary channel and subaqueous levee;In the period of Es₂⁷?Es₂⁴,the lake are basically withdrawn from the area and develops delta plain facies,the main sedimentary microfacies include distributary channel,onshore natural levee and crevasse splay;Es₂^3Es₂² sand groups develops braided river delta plain deposit,including braided channel,river island and natural levee.The river diversion is fast and the continuity is relatively poor.In the end of Es₂,The water level began to uplift gradually and transfer into shore-shallow lake facies.Based on the study of the sand bodies superimposed type and the combination pattern,it is clear that there are five kinds of boundary markers for the sand body of the delta front:the mudstone between mouth bar,dam margin deposit,difference of elevation between top and bottom,the sand body shows"thick-thin-thick"characteristics,the sand body showed obvious lateral overlap.There are mainly two splicing style of sand body:A single distributary channel splice with mouth bar,single mouth bar splice with mouth bar.And then establishes three combination styles of sand body:dam body-dam body,dam body-dam edge-dam body,mouth bar-mud-mouth bar,which lays the foundation for the study of interlayer distribution and digging residual oil.