Research On Prediction Of Sedimentary Sand Bodies And Prediction Of Favorable Target Area Of The Fourth Sand Formation Of The Fourth Member Of Shahejie Formation In Yi 176 Area,Bonan Depression

Bonan sag is located in Zhanhua Sag in the north of Jiyang depression,which is the largest secondary sag in Zhanhua sag.Bonan sag is rich in crude oil,reaching more than 1×10~8t,with good development potential.The upper sub member of Shasi is the main development interval of Bonan sag,which is divided into four sand groups.There are many researches on the sedimentary characteristics of the first sand group,the second sand group and the third sand group,and the reservoir distribution,but few researches on the fourth sand group.Therefore,it is of great significance to carry out sequence characteristics,sand body distribution and favorable area prediction for the high-efficiency development of the reservoir in the upper sub member of Shasi formation.Based on the investigation of regional data,according to core observation,drilling and logging data,test and analysis data,this paper has carried out the study of sequence division,sedimentary characteristics and sand body distribution of the upper Shasi formation in block Yi 176 of Bonan sag.Combined with reservoir exploration practice and comprehensive research results,the favorable target area of the fourth sand formation in this area is predicted,and the following results are obtained.First of all,according to sequence theory,combined with core analysis and sequence stratigraphic analysis of single well and connected well,the fourth-order stratigraphic sequence boundary(SQ)of the fourth upper sub member of Shasi formation in Yi 176 block of Bonan sag is identified,and the fourth-order sequence of the fourth-order formation is divided into SQ1,SQ2,SQ3 and SQ4.Therefore,SQ1and SQ2 sequences are missing in some well areas,SQ3 and SQ4 sequences are developed in the whole fourth sand formation.According to the characteristics of the block sedimentary background,it is clear that the sedimentary facies of the Sisha formation are fan delta facies(fan delta front subfacies)and nearshore underwater fan facies(fan middle,fan end and fan root subfacies).Due to the action of Chengdong uplift and Gudao uplift,the fourth sand formation formed two sets of sand bodies,namely fan delta front subfacies sedimentary sand body and nearshore underwater fan sedimentary sand body.The formation period and scale of different sand bodies are different.The fan delta front subfacies sedimentary sand bodies are developed in different sedimentary periods and have a large scale.They are the dominant sand bodies of the fourth sand formation.Offshore subaqueous fan sedimentary sand body developed only in SQ3 and SQ4sedimentary period,and its scale is relatively small.Combined with the interpretation data of oil layer,the distribution of oil layer is studied.In the SQ1,SQ2 and SQ3 sedimentary period,only the fan delta front subfacies sand body developed oil-bearing reservoir,the reservoir thickness is generally 2?4m,only well Yi 178 and well Yi 185 are more than 6m.In SQ4sedimentary period,a new set of oil-bearing reservoir was added in the offshore subaqueous fan sand body in the southeast of the block.Finally,based on the research results of sedimentary facies,sand body distribution and oil-bearing degree of the sand body of the fourth sand group,the class I,II and III favorable areas of the fourth sand group are determined.Among them,the sand body thickness and oil layer thickness of class I favorable area are the largest,and the oil-bearing degree is the highest,mainly located near well Yi 178 and well Yi 185.