Research On Reservoir Characteristics And Diagenetic Evolution Of Carboniferous Andesite And Volcanic Breccia In Xi'quan Area,Junggar Basin

The Carboniferous volcanic rocks in Junggar basin are rich in oil and gas resources and have good prospects for oil and gas exploration and developmen,while volcanic rocks are widely distributed and the lithology is complex and diverse.Domestically,volcanic rocks are classified as a class in general at present,which are analysed the reservoir characteristics and diagenetic evolution with ignoring the difference essence formation reasons,petrologic feature and diagenetic evolution between volcanic breccia and volcanic lava.Researchers have deeply researched the pore types and diagenesis of sedimentary rocks,which are similar to volcanic breccia,Unfortunately,we actually lack the relative information of volcanic lava.In addition,there is a relative lack of research data on reservoir characteristics,diagenesis,hydrocarbon filling and influence on pores of volcanic rocks in the Xi'quan area in the north of the Beisantai uplift in the east of the Junggar basin.So we selected the Carboniferous andesite and volcanic breccia of the Xi'quan area in eastern of Junggar basin as the research object on behalf of volcanic rocks and pyroclastic rock in this study,we thoroughly analysed the reservoir characteristics?diagenesis and diagenetic evolution of it,based upon the observation and description of drilled cores,the identifications and quantitative statistics of primary and secondary minerals and pore types,the measurement of porosity and permeability,image pore throat of andesite and volcanic breccia,X-ray diffraction for clay minerals under scanning electron microscope,and analysis of homogeneous temperature,chemical composition and fluorescence of diagenetic liquid inclusions in andesite and volcanic breccia to study the different reservoir characteristics of andesite and volcanic breccia,the diagenetic evolution sequence,hydrocarbon charging period and scale and its effect on reservoir performance,combined with the buried thermal evolution history of Xi'quan area to roughly determine the time of hydrocarbon accumulation and the formation of diagenetic minerals(Late-born quartz,carbonate).After all,we constructed the diagenesis-hydrocarbon filling-pore evolution process of Carboniferous andesite and volcanic breccia in the Xi'quan area.The study showed that andesite and volcanic breccia have commonalities and differences in genesis,mineralogical composition,pore types and pore composition,reservoir physical properties and diagenetic evolution process.The andesite reservoir space is mainly consisted of dissolving and expanding pores,platelet-soluble pores,matrix-solution pores,and a small amount of structural fractures and dissolution joints.The volcanic breccia mainly composed of intergranular dissolved pores and interstitial dissolved pore structure cracks.Stomatal andesite and volcanic breccia have many pore types and various pore combinations,its porosity and permeability,and pore structure are higher than dense andesite and tuffaceous breccia.volatilization of the volatiles determines the size of the primary pores of andesite and has little effect on the volcanic breccia reservoir space,compaction has little effect on the reservoir performance of Andesite,but it reduces the number of pores and the size of pores in volcanic breccia.Weathering and leaching,dissolution and tectonic action are the most important constructive diagenesis to improve the physical properties of andesite and volcanic breccia,while the secondary filling and cementation are largely destroyed the reservoir space and seepage mechanism of andesite and volcanic breccia which are the most important destructive diagenesis.