Reservoir Evaluation Of Chang 4+5-6 Oil Reservoir Of Yanchang Formation In Zheng 359 Well Area Of Zhidan Oilfield In Ordos Basin

The reservoir is the important factor for controlling the oil and gas accumulation and distribution,research on reservoir characteristics is an important part of oil and gas exploration.lt is the soul of low permeability oil and gas reservoir exploration and development,and an indispensable part of the reservoir description work.In this paper,Chang4+5-6 oil reservoir of Yanchang Formation in the Zheng 359 well area of Zhidan oilfield is research object,based on reservoir geology,reservoir sedimentology and logging geology as theoretical direction,by using core observation,logging data combined with a variety of experimental testing technology,the characteristics of reservoir lithology,physical property,heterogeneity,pore structure and diagenesis are studied,and analyzed the controlling factors of reservoir physical properties.The reservoir is classified and evaluated based on the above research and selected favorable zone.The delta front is mainly sedimentary face in the Chang4+5-6 sedimentary period.The underwater distributary channel sandbodies in the delta front is Northeast direction,Sand bodies are superimposed.The rock type is mainly feldspar sandstone.Detrital composition is dominated by feldspar and quartz,followed by biotite and lithic.The main materials are mica,chlorite,calcite and dolomite,containing a small amount of pyrite,siliceous and felsic.The contact between the particles are the main line and point-line contact.The types of cementation are main pore cementation,thin film cementation,film-pore cementation and enlarged pore cementation.The pore type of Chang 4+5-6 reservoir is mainly intergranular pore and dissolved pore.The average porosity of Chang 6 reservoir is about 10.2%,and the average permeability is about 1.08?m2;the average porosity of Chang4+5 reservoir is about 9.9%,and the average permeability is about 1.09?m2.The physical properties of the Chang 4+5 and Chang 6 reservoirs are poor and the heterogeneity is strong,belonging to extra low porosity and extra low permeability reservoir.Chang 4+5-6 reservoir mainly experienced compaction,cementation and dissolution,being in the A integral of late diagenetic stage.The Chang 4+5-6 reservoir sand body is controlled by subaqueous distributary channel of delta front obviously,and chlorite films cementation and dissolution are the main factors for the formation of relatively high permeability reservoirs.Micro fractures have a certain effect on the improvement of reservoir physical properties.On the basis of the above research,the reservoir classification and evaluation are carried out in combination with the sedimentary facies,sand body thickness,reservoir physical property,drainage pressure and pore throat characteristics.The Chang 4+5 and Chang 6 have I,II and III reservoirs,the other layers are dominated by II and III reservoirs.