Reservoir Evaluation Of Cretaceous Beach Bar In Block Pai 688 Of Chepaizi Area

The Chepaizi area is located in the northwestern margin of the Junggar Basin,and the Block 688 is located in the northeastern part of the Chepaizi area.The Cretaceous is dominated by the shallow lake sediments.The Cretaceous beach bar reservoir in the Block 688 has good exploration potential,but due to the serious interbedded layer of sand and mud,the thickness of the reservoir is thin,the distribution of reservoirs is unclear,and the physical properties are different,leading to favorable reservoirs.The distribution is not clear.In view of the existing problems,this paper studies the sedimentary characteristics,reservoir characteristics,reservoir distribution and physical characteristics,reservoir heterogeneity,and reservoir comprehensive evaluation of the beach bar reservoir,and has achieved the following results.The following achievements and understandings were achieved:(1)The sedimentary facies types of the Cretaceous in Block 688 were determined and the spatial distribution of the sedimentary facies was clarified.The Cretaceous is mainly developed in the shallow lake sediments.The shallow lakes are divided into the beach sand subfacies and the bar sand subfacies;the bar main microfacies develop siltstone and fine sandstone,and the single layer has a large thickness.Bar main microfacies are located in Pai 611-Cheqian 1-9 of Lianmuqin Formation,Pai 611-Pai 639 of Hutubi Formation and Pai 611-Cheqian 1-9 of Qingshuihe upper member.The Shengjinkou Formation have a small number of bar bodies near Pai 602 and Pai 611.(2)Explain the reservoir characteristics of the bar foundation of the Cretaceous.The lithology of the Cretaceous beach bar is mainly silty mudstone,gray siltstone and siltstone.From the upper section of the Qingshuihe upper member to the Lianmuqin Formation,the maturity of the reservoir rock composition is gradually reduced.The diagenesis is mainly characterized by calcite cementation.In some areas,secondary pores are produced by dissolution,and compaction is weak.The diagenesis stage of reservoirs is mainly distributed in the early diagenetic stage B.(3)The sand body micro-phase of the Cretaceous beach bar reservoir has large thickness,wide extension range and good lateral continuity.The bar side micro-facies and beach sand subphase sand bodies are thin and the lateral continuity is poor.The Lianmuqin formation developed sand bodies with large thickness and good continuity in the vicinity of Pai 68 and Cheqian 1-9,but the physical properties were poor.The sand bodies of Shengjinkou formation developed less in the study area,and the reservoir quality difference.The Qingshuihe upper member has a thickness of 25 m in the vicinity of Pai 611 and Cheqian 1-9,and the porosity is good.The sand body of the central Pai 601 to Pai 611 in the middle part of the Hutubi formation,and the sand body near the eastern boundary are thicker and have good reservoir physical properties.(4)Explain the heterogeneity characteristics and controlling factors of the Cretaceous beach bar reservoir.The heterogeneity of the reservoirs of the Lianmutun and Shengjinkou Formations is generally strong,and the heterogeneity of the Lianmuqin Formation near the Pai688 and the Shengjinkou Formation in the vicinity of the Pai 611 and the Pai 629 are the strongest.The heterogeneity of the Hutubi formation is moderately moderate,and the heterogeneity of the western boundary of the study area is strong;Qingshuihe upper member is characterized by medium-strong heterogeneity.Compaction and cementation are the main factors affecting the heterogeneity of the Cretaceous beach bar reservoir.(5)The beach bar reservoirs in the study area can be classified into type I,type II and type III according to the multi-level fuzzy comprehensive evaluation method.The beach bar reservoirs of Lianmuqin formation are dominated by type II and type III,and type II reservoirs are mainly distributed in the eastern part of the study area.The beach bar reservoirs of the Shengjinkou formation are mainly of type III,and type II reservoirs are developed near Pai 602.The type II each bar reservoirs of Hutubi formation are mainly distributed in the west of the Pai688-Pai 639 line.The type I beach bar reservoirs of Qingshuihe upper member are mainly distributed near Pai 688.