Pore ??structure Characteristics Of The Member 8 Of The Member 8 Of The Eastern Area Of ??Sulige Gas Field And Its Influence On Seepage

This paper mainly discussed the research on the characteristics of pore structure and its effect to reservoir percolation by taking example of the He8 section reservoir of the Sulige gas field.Aiming at qualitative and quantitative analysis on the characteristics of pore structure of reservoir,a variety of technologies and methods have been used,for instance:sandstone cast thin section,scanning electron microscope,mercury injection,constant pressure mercury,nuclear magnetic resonance,and X-CT scanning.By comparing the advantages and disadvantages of each method,this paper established a research method in analyzing pore structure of He8 section reservoir.Meanwhile,the application of nuclear magnetic resonance not only quantitative tested the pore size distribution of extra low permeability sandstone samples under different effective stress and water saturation,but also the seepage pattern.Research showed that:(1)The main sedimentary facies of He8 reservoir section in eastern region of Sulige gas field is medium to coarse grained lithic quartz sandstone.Secondly is lithic sandstone.Reservoirs are tight sandstone reservoir.Clastic particle are composed mainly with quartz and lithic and feldspar content is lower than 1%.Lithic is mainly made of igneous rock cuttings,phyllite cuttings and metamorphic crumbs.The average content of fillings in reservoir is 15.1%with mainly clay,calcareous cementation.The clay mineral mainly consists of kaolinite and chlorite.(2)The average porosity of He8 section is 3.78%and the average permeability is 0.069×10-3?m2,which belongs to typical tight sandstone reservoir.The pore type of He8 reservoir is residual primary intergranular pore,intergranular dissolved pores and intragranular dissolved pore,The throat type is mainly tube bundle throat;According to the enterprise standard of Changqing Oilfield,the reservoir of He8 section are mainly II and III reservoir.(3)A comprehensive comparison of different testing methods on the characterization of pore structure,cast thin section can visually see the pore type,size,distribution and connectivity of pore and throat,However,the casting thin sections only demonstrate the two-dimensional characteristics of pore and throat,and cannot accurately quantifies test.High pressure mercury can rapidly and accurately test the distribution of pore throat and core but it cannot be used repeatedly due to environmental constraints and cannot distinguish between core pore and throat.The constant speed mercury injection is able to test the distribution of pores and throats,but test pressure is low than 7MPa,and it cannot test pores and throats of less than 0.12?m,long testing time and high cost shortcomings.Nuclear magnetic resonance can quickly test the distribution of pore throat and pore structure parameters,but the test results are easily affected by the impact of paramagnetic materials and core saturation degree.The micron scale X-CT can scan 3D pore structure directly and can reflect the characteristics of pore structure,but the accuracy is not good.The experimental data processing of complex is characterized by high cost,strong heterogeneity of the core and other disadvantages.(4)High pressure mercury test showed that the average pore throat radius is 0.1?5 ?m,the average displacement pressure is 1.459MPa and the average median radius is 0.067m.The maximum mercury injection saturation mercury withdrawal efficiency for an average of 74.87%,with an average of 43.82%.The peak of Class I reservoir is obvious,the main flow range is 0.18?4.92?m,and the mercury injection amount is 90%.Class ? reservoir is mainly distributed in Shuangfeng.The flow range of 0.18?1.45?m and the mercury injection amount is 42%.Class ?,IV reservoir showed no peak.The flow range is 0.09?0.92?m and 0.15?0.92?m,The amount of mercury is 41%and 38%.The constant pressure showed that weighted average value of throat radius was 1?3?m,the average number is 1.75?m,and the mainstream throat radius is 0.8?3?m.The weighted average of the pore throat ratio was 120?350,and the average number is 206.NMR analysis shows that the irreducible water saturation is 30%-65%.The pore size distribution is consistent with the mercury injection test.The X-CT study showed that pore connectivity rate of class ? reservoir is 16%,the coordination number is 1.85,the pore connectivity rate of class? reservoir is 36.91%,and the coordination number is 2.31.(5)Under the irreducible water condition,sample gram regression curve showed three regions:low permeability gas-solid(liquid)of slippage effect area,and low speed viscous force area of turbulent velocity region.The permeability of core decreases with the increase of water saturation.Under the irreducible water condition,when the maximum effective stress is 16MPa,the bound water of less than 0.02 is reduced by 28.44%,the bound water of higher than 0.02?m,increased by 1.12%.The lower permeability is resulted by rock pore micro deformation.