Study On Geological Effect And Logging Response Characteristics Of Petrophysical Properties Of Ultra-low Permeability Reservoir

The main tendency of oil exploration and development gradually shift to ultra-low permeability(tight reservoir)reservoir with the gradual decrease of remaining recoverable reserves of conventional oil deposit.The heterogeneity of physical property is strong and geological controlling factors are complex in Chang 6 ultra-low permeability reservoir of Wu Cangbao area in Ordos basin.So,it is necessary to find out the influence mechanism of geological factors on reservoir physical properties,such as sedimentation and diagenesis effect.The dissertation takes the Chang 6 reservoir of Wu Cangbao area as the research object,based on the theories and methods of sedimentology,petrology,reservoir geology and crystal opticalan,the intrinsic relationships of reservoir physical properties and grain size,sorting and mineral composition are detailedly discussed by using core data,outcrop data,electron microscopy data,the mercury injection experiment data,thin section data,logging data and combining with previous research results of sedimentary facies in the study area.The dissertation detailed descripted the reservoir physical properties of different sedimentary microfacies,then use geostatistics method to analyze the influence mechanisms of the factors on reservoir properties.Such as compaction,cementation,dissolution,buried depth and microfracture.Finally the logging response characteristics of ultra-low permeability reservoir property are briefly discussed.The dissertation has obtained the following conclusions and cognitions:(1)The physical property of Chang6 reservoir is bad in Wu Cangbao area,Ordos basin.The porosity of core analysis is between 3.3%~13.7%,the average is 8.2%,mainly concentrated in 6%~10%;The permeability is between 0.04~1.19 mD,the average is 0.28 mD,the permeability is less than 0.4 mD of 75% of the sample,it is belong to typical low permeability reservoir.(2)Deposition has a certain influence on reservoir property.Sedimentary microfacies is the comprehensive reflection of specific water environment about the particle size and sorting characteristics,mineral components,these characteristics have a direct relationship with reservoir property.The research showed underwater distributary channel microfacies,debouch bar microfacies,as the main sand framework among them,often the particle separation of the reservoir is relatively good,the clastic is given priority to fine particle and medium particles in coexistence,the reservoir physical property is better,the porosity is 8% on average,the permeability is 0.32 mD on average;River edge microfacies is less than that,the porosity is 6% on average,the permeability is 0.18 mD on average;The between distributary bay microfacies is given priority to silt particles,shale content is higher,the reservoir physical property is bad,most of the porosity is less 5%,the permeability is less than 0.1mD.(3)Diagenesis have great influence on reservoir physical properties.Chang 6 strata was deep buried,lead to the formation suffered the intense compaction,and make the rate of porosity loss to 52%;For the Chang 6 strata,temperature is higher,and with high content of unstable mineral components,the change of pore fluid,lead to the dissolution,metasomatism and cementation are intensive in the area.The dissolution,metasomatism take constructive role of pore in the reservoir,the product of cementation occupy the pore space,plug throat,have great destructive to reservoir property.The rate of reservoir pore loss made by diagenesis in study area is 33% on average.In addition,the development of cracks make the reservoir permeability has greater improvement.(4)The dissertation analyzed the interpretation for porosity model with conventional logging and nuclear magnetic logging,nuclear magnetic logging permeability interpretation model application effect is better and the interpretation accuracy is higher in ultra-low permeability reservoirs.