The Comprehensive Evaluation Of Tight Sandtone Reservoir And Structure Of Chang 9 Oil Reservoir In Zhouchang Area,Ordos Basin

Triassic tight reservoirs are widely distributed in Ordos Basin.It is vital to build a suitable logging comprehensive evaluation system for tight reservoir for judging the quality of tight reservoir,accurately calculating the geological reserves and locating the distribution of tight oil.This study takes the Triassic Yanchang Formation Chang 9 tight reservoir in the Zhouchang area as the object,on the basis of application of laboratory data,geological data and production data,we studied the petrological characteristics,micro pore structure,reservoir physical properties and heterogeneity,analyzed the main factors controlling the physical properties of the tight reservoir,reestablished the calculation models of porosity,permeability and saturation of tight reservoir,determined reasonable cutoff values of effective reservoirs,and established the logging identification standard for tight oil.The plane distribution maps of porosity,permeability,oil saturation were made in order to master the vertical and plane distribution characteristics.The author established a multi-parameter comprehensive evaluation standard for tight reservoir and classified the reservoirs.Made the following understanding:The Chang 9 member,whose stratum is relatively flat,with nose like uplift and small dorsal uplift in the near northeast direction,can be divided into two sub-units.This article recognize two main sedimentary microfacies in the study area,underwater distributary channel and subsea interdistributary bay.The main type of the sandstone is feldspar and debris-feldspar sandstone,the mean amount of interstitial material is 10.1%.The intergranular pores are the primary reservoir spaces,followed by local structural fractures.The reservoir pore structure can be divided into three categories,and the?-type,medium displacement pressure and small pore-fine throat type,is predominant.The reservoir of Chang9,median porosity 8.4%and median permeability 0.40×10^-3?m²,is of typical ultra-low porosity and tight reservoir with strong heterogeneity.The physical properties are affected together by the parent rock in the source area,sedimentary facies,diagenesis and tectonic processes.Sand body scale,physical properties and lateral facies changes are the main factors controlling reservoir distribution,and local nose structurs play a certain role in reservoir formation.On the basis of curve standardization and core homing,shale content and calcium content can be calculated separately by the multivariate functions of spontaneous potential,natural gamma ray,acoustic time difference and deep induction resistivity,who are sensitive to mud and calcium content.The mud content is 8%and the calcium content is 17.3%in the study area.The porosity can be obtained from the three-dimensional regression equation of acoustic time difference,shale content and calcium content.By calculation,it is found that the calcium content has little effect on porosity and can be ignored.The porosity change caused by the mud content is about 0.6%,and generally mud content cannot be ignored.The value of permeability can be obtained by the function of porosity and shale content.The tight oil saturation logging calculation model is established by dividing the rock experimental data are divided into two groups by porosity of 7%,and the tight oil saturation of each group is calculated through different saturation formula.The cutoff values of physical properties of Chang 9 effective reservoir are determined by empirical statistical method,as permeability0.15×10^-3?m²and porosity 6.0%.The resistivity of the oil layer is generally larger than27.0?·m,when the acoustic time difference is less than215.0?s/m,the reservoir contains no fluid and is treated as dry layer.Eight parameters,porosity,permeability,effective thickness,sandstone thickness,storage coefficient,oil storage coefficient and formation coefficient are optimized as the evaluation parameters.Using weight analysis method,we carry out single-well quantitative evaluation respectively on the two layers of Chang 9.Combined with semi-quantitative analysis of sedimentary microfacies,pore types,production data,etc.,Chang 9 tight reservoir is divided into three types,of which?-type reservoir is the key development object in the future.