Study On The Characteristics And Control Factors Analysis Of The Chang 7 And Chang 8 Tight Sandstone Reservoir In Nanniwan Oilfield

The research on sandstone reservoir of Chang 7 and Chang 8 is relatively weak in Nanniwan area,in Ordos Basin,especially on factors which control the reservoir storage properties.Therefore,it is necessary to carry out reservoir characteristic research on Chang 7 and Chang 8 in Nanniwan Oilfield to provide the geological basis for further exploration and development.This paper goes on to research and discuss the characteristics of petrology,microscopic reservoir characteristics,and diagenesis and reservoir physical properties of the Chang 7 and Chang 8 reservoir in Nanniwan Oilfield.In this process,this paper analyses these points by means of methods under the guidance of sedimentology,reservoir sedimentology and oil geology.The methods include the detailed description and observation of drilling cores,and observation of thin-section of the cast,analyses of X-ray diffraction,cathode luminescence image,electron scan microscope,capillary pressure and.After the comprehensive research of reservoir,the paper holds that:The componential and textural maturities of the sandstone in the Chang 7 and Chang 8 formation is lower and lithological types are mostly fine-grained arkose,which the interstitial matter is widespread but not uniform distribution.The type of cements observded includes carbonate and clay minerals.Diagenesis types include compaction,cementation,metasomatism,dissolution and fraction.The diagenetic evolution of the sandstones is mainly in the A phase of the middle diagenetic period.It is mainly intergranular dissolution pore of Chang 7 reservoir and intergranular pore and residual intergranular pore of Chang 8 reservoir.The physical properties research shows that average porosity is 7.62% and average permeability is 0.28×10^-3μm² of Chang 7 reservoir;average porosity is 7.79 % and average permeability is 0.32×10^-3μm² of Chang 8 reservoir.Overall,reservoirs of Chang 7 and Chang 8 belong to extra low permeability and super low permeability reservoirs.The distribution of high quality reservoir is mainly affected by sedimentation control,which shows that properties in underwater channel is better;diagenesis of compaction and cementation are two main factors to reduce the reservoir storage properties and secondary pore,such as feldspar dissolved pore,generated by the dissolution,is the main factors to enhance the reservoir storage properties.