Densification Genesis And Prediction Of Sandy Conglomerate Reservoir Of Badaowan Formation In Well AH5 Area Of Junggar Basin

Aihu 5 well block in the west slope area of Mahu Sag in Junggar basin has favorable reservoir forming conditions.In recent years,a major breakthrough has been made in Badaowan Formation of Lower Jurassic,reflecting that Badaowan Formation has great potential for oil and gas exploration and development.Badaowan Formation in the study area belongs to sandy conglomerate reservoir with low saturation,ultra-low porosity and ultra-low permeability.In order to promote the further exploration and development of oil and gas in Badaowan Formation in this area,it is very important for the prediction of reservoir"dessert",and the densification analysis of sandy conglomerate reservoir is an important basis for the prediction of"dessert".Based on the systematic summary of previous research results of relevant sandy conglomerate reservoirs,combined with more than 100 meters of continuous core observation and microscopic thin section observation,this paper simplifies the reservoir rock types of member 5 of Badaowan Formation into sandy（gravel particle volume fraction<50%,including gravelly medium coarse sandstone,fine medium sandstone and fine sandstone）and gravelly（gravel particle volume fraction>50%,including conglomerate,sandy conglomerate and sandy conglomerate）.The components of reservoir rocks are analyzed in detail by X-ray diffraction and thin section observation;Based on the above lithology classification,a large number of cast thin sections and scanning electron microscope data are used to analyze the pore space type of the target reservoir in detail;Using physical properties and mercury injection data,the development characteristics and vertical evolution of physical properties of reservoirs with different lithology are clarified.Combined with the oil test data,summarize the oil-bearing properties of reservoirs with different lithology and analyze the oil-bearing characteristics of favorable reservoirs;Using a large number of cast thin sections,mercury injection curves and basic parameters,the pore structure of reservoirs with different lithology is analyzed quantitatively and qualitatively;Based on the study of reservoir characteristics,clarify the types of reservoir diagenesis and diagenetic evolution sequence,reveal the quantitative influence of different diagenesis on reservoir pores,and summarize the reasons for reservoir densification;Finally,on the basis of the above research,summarize and describe the types and characteristics of high-quality reservoirs,summarize the control factors of high-quality reservoirs,and predict the development area of high-quality reservoirs,so as to provide guidance for the further exploration and development of subsequent target reservoirs.The specific research results are as follows:（1）According to the gravel content,the target reservoir is divided into gravel reservoir and sandy reservoir,and the overall composition maturity and structure maturity are low.J₁b₅reservoir belongs to ultra-low porosity and low permeability reservoir as a whole.The gravelly reservoir is dominated by intragranular dissolved pores,and the throat is dominated by lamellar and lamellar curved throat;The reservoir space of sandy reservoir is mainly residual intergranular pores,intergranular dissolved pores and intragranular dissolved pores,and the throat is mainly lamellar and lamellar curved throat.The oil-bearing heterogeneity of the reservoir is strong,and the oil saturation of sandy reservoir is higher than that of gravel reservoir.Using fractal dimension and basic parameters of mercury injection to characterize the pore structure,it is found that the pore structure of sandy reservoir is better than that of gravel reservoir,which reflects that the oil saturation of reservoir is mainly controlled by the pore structure.（2）J₁b₅reservoir belongs to middle diagenetic stage and a-late diagenetic stage.Compaction and cementation have the most obvious influence on physical properties in gravel reservoir,and dissolution has less influence on physical properties;In sandy reservoir,compaction,cementation and dissolution have obvious effects on reservoir physical properties.（3）Under the sedimentary background of low overall composition maturity,the original porosity of J₁b₅reservoir is poor,and the later compaction and cementation make the reservoir compact.Among them,compaction is the main reason for reservoir densification,while cementation is the key to further densification,and dissolution is more important to improve the densification of sandy reservoir.（4）The formation of J₁b₅high-quality reservoir in the study area is controlled by sedimentation and diagenesis.Based on the division of daily liquid production,according to the reservoir lithology,combined with porosity,permeability and basic parameters of mercury injection,J₁b₅reservoir is divided into three categories:I,II and III by focusing on fractal dimension.Using Fisher discriminant method,the discriminant functions of different types of reservoirs are established.Combined with the logging data of multiple wells,the plane distribution map of different types of reservoir thickness is drawn.