The Research Of Reservoir Characteristics Of The Fourth Member Of Xujiahe Formation Of Yuanba Area In Northeast Of Sichuan Basin

Because the rolling exploration and development was used in Yuanba Gas Field in Northest of Sichuan basin,and the early stage of the exploration focuses on marine strata,the Xujiahe Formation have not been explpored as the key center of object.In recent years,the continental strata formation shows good testing results,showing that continental strata formation has a good prospect of exploration and development.But the gas reservoir of the fourth member of Xujiahe Formation is complex,and reservoir matrix property is poor,and heterogeneity is strong,and reservoir space distribution and influence factors of development needs to be improved.So,in order to improve the rate of producing gas and high efficient production,and to develop the fourth formation gas reservoir well reasonably.On the basis of core,casting thin sections,scanning electronic microscope,well logging,borehole log,testing and commission of gas and other information,combined with the results of previous studies,this paper studies the sedimentary facies,the distribution of sand and conglomerate laryer,reservoir characteristics,diagenesis types and characteristics of the fourth member of Xujiahe Formation,and then preliminarily discusses the influence of deposition and diagenesis on reservoir physical property.Moreover,the lower limit standard of reservoir physical property of the fourth member of Xujiahe Formation has been established and the classification and distribution of reservoir has been evaluated in this paper,and the following research and understanding has been made.1?According to coring,borehole log,well logging comprehensive interpretation,combining previous research results,the study shows that the four phase of Xujiahe Formation is fan delta-lake sedimentary environment.The main sedimentary microfacies include braided distributary channel,underwater distributary channel,distributary bay and mouch bar.The favorable facies belt for the development of reservoir area is braided distributary channel,underwater distributary channel and mouth bar.2?The distribution pattern of sand and conglomerate presents the following characteristics:the conglomerate is mainly distributed in the western of the area,and the sandstone is mainly distributed in the central and east;Conglomerate mainly distributed in the upper section of the fourth member of Xujiahe Formation,and sandstone mainly distributed in lower section of the fourth member of Xujiahe Formation;Conglomerate are mainly distributed in the braided distributary channel,and sandstone mainly distributed in underwater distributary channel.3?Based on casting thin sections,core and so on,the paper analysis that sandstone type of the fourth member of Xujiahe Formation mainly is fine-mesograin lithic sandstone,followed by feldspathic lithic sandstone and lithic quartz sandstone;the type of conglomerate mainly is fine-mesograin glutenite and conglomerate,and gravel composition is mainly carbonate rocks,followed by siliceous rocks and sedimentary quartzite.Reservoir space types mainly is intragranular dissolved pore and intergranular dissolved pore.4?The type of diagenesis mainly include compaction/pressolution,cementation,dissolution,metasomatism and cataclasis.And the diagenetic evolution degree is high,and the diagenetic stage of the purpose layers have been late diagenetic B stage.5?Sedimentation and diagenesis jointly affect the development of reservoir of the purpose layers.Sedimentation controlled the macro distribution of reservoir development.Compaction and cementation are the important factors that affect reservoir densification,and dissolution is the key factors of the secondary pore development of reservoir levels.6?The lower limit of the porosity of the four member of the Xujiahe Formation is defined as 3%,and the lower limit of the permeability is defined as 0.03 md.The types of reservoir can be divided into four types,and its distribution presents the following characteristics: the development degree of the lower section reservoir of the four member of the Xujiahe Formation is more higher than the upper section;the development degree of the central and eastern reservoir of the area is more higher than the western reservoir,fouthermore the type of the central and eastern reservoir of the area mainly is II and III,and local area is I,but the type of the western reservoir of the area mainly is III.In addition,the distribution of the lower section reservoir of the four member of the Xujiahe Formation is more larger,and the thickness is more bigger than the upper section.The development degree of conglomerate reservoir of the Xujiahe Formation is poor,develop only in the individual sections.