Main Controlling Factors Of Favorable Reservoirs In The Shahejie Formation Of Paleogene In The Northern Part Of Liaoxi Sag,Bohai Bay

The Liaodong Bay area is one of the important oil and gas producing areas in the Bohai Sea.However,the exploration degree of the Shahejie Formation in the northern slope of the Liaoxi Depression is relatively low,and the characteristics of diagenesis and reservoir is not clear.At the same time,there is no complete reservoir evaluation standard,and the analysis of favorable reservoir control factors is not clear enough,which restricts further oil and gas exploration in this area.On the basis of microsection,scanning electron microscopy,core observation,inclusions,X-ray diffraction,Ro,mercury pressure data to analyze the reservoir of Shahejie formation in the northern slope of the Liaoxi Depression.Through core observations,well logging data and drilling data,the main sedimentary environments in the Shahejie Formation area are lacustrine sedimentary and braided deltaic sediments,The favorable reservoirs mainly develop in the microfacies of underwater distributary channels.The rock types are mainly lithic feldspathic sandstone and feldspar lithic sandstone.The main types of pores are remnant primary intergranular pore and secondary dissolution pores,and secondary pores mainly come from dissolution of feldspar.Compaction and cementation are the main diagenesis of reservoir porosity reduction.The two phases of dissolution are the key to the improvement of porosity,mainly feldspar dissolution.Through the analysis of clay minerals,inclusion temperature and Ro,the final diagenetic stage is middle diagenetic A stage,and a few of them enter the middle diagenesis B stage.Based on the occurrence status of diagenetic minerals and the point counting thin section statistics,the diagenetic evolution sequence and pore evolution of Shahejie Formation sandstone are divided and established.The results shows that compaction loss of 18.63% porosity,loss rate of 58.58%,cementation loss of 7.85% porosity and dissolution provide 10.06% porosity.Through statistical analysis method,empirical statistics method,well logging parameter analysis method and other methods,the reservoir classification evaluation criteria were determined.In I type reservoirs,the porosity range is greater than 19.5% and the permeability is greater than 7mD.II type reservoir porosity distribution range of 15%-19.5%,permeability range of 2mD-7mD.The III type reservoir is the worst with a porosity of less than 15% and a permeability of less than 2mD.The favorable reservoirs are controlled by sedimentation and diagenesis.The underwater distributary channel and mouth bar with high energy facies has less intergranular interstitial and with more quartz rigid particles,the compaction is weak,which is the basis for the formation of favorable reservoirs.The further superposition of the later feldspar dissolution is the main reason for the formation of favorable reservoirs in the study area.