Research On The Beneficial Reservoirs Of The Lower Assemblage Of Yanchang Formation In Fuxian Exploration Area,Ordos Basin

Fuxian area of Ordos Basin is rich in oil and gas resources,but the overall exploration and research level is still in the primary stage.Based on petroleum geology,sedimentology,reservoir geology and logging geology,the types and characteristics of sedimentary microfacies in the study area are analyzed,and the distribution of sedimentary facies and sand body in the lower assemblage of Yanchang Formation in Fuxian exploration area is discussed.Guided by the data of core,mud logging and well logging in the study area,the Chang9～Chang 7 reservoirs of Yanchang Formation in the study area is analyzed from the aspects of lithology,sedimentary environment,reservoir physical properties,pore types,structure and diagenesis by using the identification results of microscopic slices,X-ray diffraction clay mineral content analysis and laboratory experiments such as scanning electron microscopy and mercury injection test.Reservoir characteristics of formation.Based on the above results,the favorable distribution range of sandstone reservoirs in Chang 9～Chang 7 reservoirs in the study area is further predicted.The study shows that Delta and lacustrine sedimentary systems are developed in Chang 9,Chang 8 and Chang 7 reservoirs of Yanchang Formation in Fuxian exploration area.The rock types are lithic feldspar sandstone and feldspar clastic sandstone,which are characterized by fine grain size,low compositional maturity and medium structural maturity.The grinding roundness is mainly sub-angular-sub-circular,the sorting degree is above average,and the contact between particles is mostly point-line.The main type of cementation is porous cementation,the main pore is intergranular pore,followed by feldspar dissolved pore,and the pore structure is mainly medium pore and fine throat,small pore and fine pore and micro throat.Chang 9～Chang 7 reservoir is mainly composed of ultra-low permeability reservoir and ultra-low permeability reservoir.The reservoir of Chang 9～Chang 7 reservoirs is evaluated by comprehensive factors of sedimentary facies,sand body distribution and reservoir physical properties.The distribution range of all kinds of favorable reservoirs in Chang 9～Chang 7 reservoirs is predicted.There are mainly class II favorable reservoirs and class III favorable reservoirs in the study area,while class I favorable reservoirs are relatively less developed.This provides a reliable geological basis for the exploration and development of the lower assemblage of Yanchang Formation reservoirs in the future.