Study On Sedimentary Microfacies And Reservoir Characteristics Of Chang 8 In Well Z Area

Ordos Basin is one of the large oil and gas-bearing basins in China,which contains rich oil and gas resources.The Z well area in Dingbian area is located in the middle and west of the Yishan slope of Ordos Basin,and the Chang 8 oil formation group is a focus of oil and gas development work in recent years,which has good prospect of oil and gas exploration.However,it is difficult to explore due to its large burial depth,therefore,it is important to conduct the study of sedimentary micro-phase and reservoir characteristics for oil and gas development and increase production and efficiency.In this paper,based on core,logging and analytical test data,we combine stratigraphy,sedimentology,logging principles and other multidisciplinary research to establish a stratigraphic comparison and a stratigraphic grid by dividing the Chang 8 reservoir in the Z well area into two substrata,Chang 8₁and Chang 8₂,using the marker layer method and stratigraphic thickness.Through sedimentary phase markers and logging curve features,it was determined that the Chang 8 reservoir develops deltaic foreland subphase,which can be further divided into four microphases:submerged divergent channel,divergent interbay,estuarine dam and submerged natural dike.The Chang 8 reservoir sandstone is mainly a set of gray fine sandstone,and the rock type is dominated by rock chip feldspathic sandstone and feldspathic rock chip sandstone.The pore type is mainly intergranular pores,with a face porosity of 2.90%,accounting for 70.2%of the total face porosity.The reservoir diagenesis includes compaction,compressional solution,cementation,dissolution and accounting,and compaction and cementation are the main reasons for the dense reservoir in the Chang 8reservoir.The average porosity of the Chang 8 reservoir is 8.09%and the average permeability is 0.49×10^-3μm²,which is an extra-low porosity-ultra-low permeability reservoir.On the basis of sedimentary microphase and sand body spreading,combined with rock type,pore structure and diagenesis,the Chang 8 reservoir in Z well area is classified into four types:type I is a good reservoir,type II is a better reservoir,type III is an average reservoir and type IV is a poor reservoir,among which,type II and type III reservoirs have the largest distribution range.