| Taking the Zhiluo Formation of Middle Jurassic in the Yanchang exploration area of the Ordos Basin as the research object,comprehensively using the structural knowledge of sedimentology,sedimentology,petrology,reservoir geology and well logging interpretation,through conventional geological analysis methods,the stratigraphic division contrast,sediment and sand body distribution,series analysis of reservoir characteristics and other studies to carry out research and comprehensive analysis of reservoir influence factors.Finally based on previous studies on sedimentation,diagenesis and reservoirs in the study area,taking effective thickness,porosity,permeability,sedimentary facies,displacement pressure,and sorting coefficient as parameters to establish the reservoir evaluation criteria in this area by stages.By dividing and comparing the strata in the study area,the Zhiluo group is divided into upper and lower sections.The average thickness of the upper and lower strata is 135m and150m,respectively,and it has the characteristics of"thin lower and upper thin,west thick and east thin".The structure as a whole is a gentle west-dipping monoclinic,with a sharp extinction line on the Ansai-ganquan.Further sedimentary facies analysis shows that the lower section is dominated by braided river-braided river delta deposits,and the upper section is dominated by meandering river-meandering river delta deposits.There are shallow lake facies and delta deposits in the southeast of the study area,with sand bodies connected The film is good.In general,the main sedimentary microfacies are river channels,heart beaches,side beaches,floodplains,underwater distributary channels and distributary bays,and the dominant phases are channel filling in braided river subfacies,heart beach microfacies and meandering river subfacies.The microfacies of the river channel and the side beach control the development of the reservoir in the study area.The lithology of the Zhiluo Formation in this block is dominated by feldspar sandstone,and the roundness is mostly sub-angular.The separation is good,the composition maturity is low,and the structural maturity is medium-good;Dissolved pores are the main storage space.The throats are mainly lamellar or curved lamellae and tube bundle throats.The types of pore is mainly a combination of dissolved pores and intergranular pores.The reservoir heterogeneity is extremely strong,the maximum porosity is 22.1%and the minimum is 6.8%,and the average porosity is 17.27%;the maximum permeability is 600×10-3?m2,the minimum permeability is 0.09×10-3?m2,and the average permeability is 202.8×10-3?m2.The sandstone reservoirs with low porosity,ultra-low porosity,medium-low permeability and ultra-low permeability are developed.The diagenetic evolution of the Zhiluo formation in this block goes through the early diagenesis stage A,the early diagenesis stage B,the meteorite stage A,and the transformation stage to B stage of middle diagenesis.The pore loss is 28.47%.The destructive diagenesis with compaction and cementation and the constructive diagenesis with dissolution and rupture restrict the physical properties of the reservoir.The Zhiluo Formation Reservoir is mainly affected by sedimentary microfacies,clastic particle composition and particle size,pore structure and diagenesis;sedimentation is the internal cause,and later diagenesis directly controls the changes of reservoir physical properties.The upper and lower sections of the reservoir in the study area are divided into three types:Type I is the high-quality reservoir of Zhiluo Formation,Type II is the medium-grade reservoir of this group,Type III is the poor-grade reservoir of this group,and Type I and II reservoirs are widely distributed. |
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