The Study Of Diagenetic Facies Of The Chang 9 Reservoir In The Nanliang Oilfield,Ordos Basin

The maturity of oil and gas exploration of the Chang 9 oil-bearing bed(Chang 9)is relatively low at the Nanliang Oilfield in the Ordos Basin.Although the preliminary exploration work and oil test data have identified that some wells in the Chang 9 have production,the reservoir properties,their controlling factors and favorable areas of the Chang 9 is still unclear,which cannot promote oil and gas development.Diagenesis is the key element influencing the tight sandstone reservoir’s quality.The study of diagenetic facies implies a more systematic and detailed study of the reservoir from the perspective of genesis.In this study,casting thin sections,scanning electron microscopy,cathode luminescence,X-ray diffraction,and fluid inclusions were used to summarize the petrological characteristics of the Chang 9 in the research region.The Image J software and statistical analyses were used to recovere the diagenetic evolution sequence and porosity evolution of different diagenetic facies.High pressure mercury injection,nuclear magnetic resonance,and oil-water infiltration tests were adopted to study the micro-pore characteristics and seepage features of different types of diagenetic facies,and the characteristics of favorable diagenetic facies were defined.Combined with logging data,diagenetic facies of single well were identified and plane distribution of diagenetic facies were predicted.For the Chang 9,the rock granularity is primarily fine sand,mineral components are mainly composed by feldspar and quartz,interstitial materials are primarily clay minerals and carbonates,and it belongs to the ultra low porosity-ultra low permeability reservoir,and rock type is primarily lithic feldspar sandstone.The reservoir is currently at the phase of the middle-diagenetic A after undergoing compaction,dissolution,and cementation.The Chang 9 can be classified into mineral dissolution facies,clay cementation facies,silica cementation facies,and carbonate cementation facies,based on physical features,degree of diagenesis,types of diagenetic minerals and main types of diagenetic processes.The corresponding characteristics of various diagenetic facies in DEN,AC,GR,RT,and CNL logging curves were analyzed,and the logging plates for differentiating different diagenetic facies were established.The pore evolution progress,micro-pore characteristics,saturation of movable fluid and oil-water relative permeability in different diagenetic facies were summarized.Through comprehensive analysis,it is concluded that the mineral dissolution facies and silica cementation facies are favorable diagenetic facies,and the type and content of minerals,physical properties and pore structure are the main factors affecting the pore structure and characteristics of oil-water relative permeability in different diagenetic facies.In the plane,diagenesis facies are dispersed in a banded pattern,with mineral dissolution facies at the channel’s center,clay cementation facies and carbonate cementation facies along the channel’s borders.