Study On Sedimentary Microfacies And Reservoir Characteristics Ofchang 7 In Y Area

In order to clarify the sedimentary characteristics and reservoir distribution law of Chang 7 of Yanchang Formation in the Ordos Basin,this paper is based on various data such as cores,logging and analytical tests,and uses theories such as stratigraphy,logging geology,sedimentology,and reservoir geology.As a guide,the sedimentary microfacies and reservoir characteristics of Chang 7 in the Y area are deeply studied.The Y area is located in the western part of the northern Shaanxi slope of the Ordos Basin.Influenced by the northeast-southwest provenance,the Chang 7 member mainly develops delta front subfacies,which are further divided into underwater distributary channel,mouth bar and interdistributary bay microfacies.Among them,underwater distributary channel sand bodies are well developed and are the main reservoir sandstones.The rock types of Chang 7 are mainly feldspar sandstone and lithic feldspar sandstone,and the interstitials are mainly clay minerals and carbonate cements.The reservoir pore types in Chang 7 are mainly feldspar dissolved pores,a small amount of residual intergranular pores and micro-fractures,and the pore throat radius is a fine throat.The statistical results of physical properties show that the porosity of Chang 7 reservoir is mainly concentrated in 8.02%～12.31%,and the permeability is mainly concentrated in 0.05×10^-3μm²～0.67×10^-3μm²,which belongs to ultra-low porosity-ultra-low permeability reservoir.The destructive diagenesis that affects the quality of the reservoir is mainly compaction and cementation,and the constructive diagenesis is dissolution.Combined with reservoir physical properties,sand body distribution and diagenesis,the reservoirs in Y area are divided into three types.The favorable reservoirs are mainly I and II reservoirs,which are mainly distributed in the main part of the underwater distributary channel.Among them,the Chang 7₂reservoir has the best physical properties,and the favorable reservoir areas are mainly distributed in the middle of the interval.