Reservoir Characteristics And Main Controlling Factors Of The Paleogene Huagang Formation In The Area E Of The Xihu Sag

The Huagang Formation of Paleogene in the Area E of Xihu Sag in the East China Sea is a tight sandstone reservoir with low porosity and permeability,and the potential for oil and gas exploration and development is huge,but its diagenetic evolution mechanism,pore evolution process and the main controlling factors of reservoir development still need to be further studied.On the basis of the previous research results and the current research situation of the research area,this paper uses various experimental test data such as conventional and cast flake identification,high pressure mercury intrusion analysis,X-diffraction clay analysis,electron probe composition analysis,fluid inclusion temperature measurement,and zircon U-Pb isotope dating analysis to analyze the basic characteristics,pore evolution characteristics and diagenetic evolution process of the Huagang Formation sandstone reservoir in Area E,and then comprehensively analyze the main controlling factors of Huagang Formation reservoir development in the study area.Based on this,it can provide enlightenment for the study of the Huagang Formation reservoir in the Area E of the Xihu Sag and the oil and gas exploration.This article mainly obtains the following points:(1)Through a large number of thin sections identification and measured physical properties and other data analysis,it is believed that the rock types of the Huagang Formation in Area E are mainly feldspathic detrital quartz sandstone,while a small amount of detrital sandstone and feldspathic debris sandstone are developed.The sandstone in the study area has a high quartz content,with the characteristics of finemedium sand,high maturity of the components,good separation,and roundness to the secondary edge-subcircle.The interstitial material has the characteristics of low matrix and low cement content,and belongs to clean sandstone.The reservoirs of Huagang Formation in Area E are dominated by ultra-low porosity and ultra-low permeability reservoirs,followed by low porosity and low permeability reservoirs.(2)According to the observation of the casting thin sections,combined with the high-pressure mercury intrusion experiment,the pore type and structure of the area were explored from different angles.There are three types of pores in the Huagang Formation in Area E: secondary pores,primary pores,and microfractures.The average porosity is 9.41%.The secondary pores,mainly intergranular dissolved pores,intragranular dissolved pores and mold pores,contribute the most to reservoir porosity.The high-pressure mercury intrusion experiment showed that the median pore throat radius,average throat radius and physical properties showed a positive correlation,and the displacement pressure,median pressure,throat sorting coefficient and physical properties showed a negative correlation.(3)According to the scanning electron microscope analysis,cathodoluminescence analysis and other technical means to explore the diagenesis characteristics of the Huagang Formation sandstone in the study area,it is believed that there are three main types of diagenesis in this area: compaction,cementation and dissolution.Based on the experimental analysis of the Ro value,the maximum pyrolysis peak temperature of the source rocks and the uniform temperature of the inclusions,the diagenetic evolution sequence of the Huagang Formation reservoir in Area E was established.The original porosity and secondary porosity of the Huagang Formation reservoir in the study area were restored and calculated,and the pore evolution process was restored,and finally the diagenesis-pore evolution model of Huagang Formation in Area E was established.(4)The reservoir development of Huagang Formation in the study area is mainly controlled by sediment source,diagenesis,rock ore composition,oil and gas charging,abnormal high pressure and other factors.The sediment source directly controls the mineral composition and structural maturity of the reservoir,providing a material basis for reservoir development.In the process of diagenesis,compaction and cementation caused the majority of pores to disappear,the multi-stage dissolution of organic acids and the dissolution of atmospheric fresh water have formed a large number of secondary pores.High quartz,low matrix content,coarser detrital particles,and better sorting and roundness are beneficial to the development of relatively high-quality reservoirs.The early oil and gas charging contains a large amount of organic acids,which can provide acidic dissolution medium,which is conducive to the formation of secondary pores.Overpressure can alleviate the pressure generated by the overlying strata,and on the other hand inhibits cementation to a certain extent.