| As this thesis'study object, JiYuan area's chang 4+5 formation is richness in oil and gas resources at Ordos which occupies important position in Chinese petroleum basins. By the multiple use of optical/scanning-electron microscope, electron probe,X-diffraction, high pressure mercury injection, the following conclusions have been obtained for the chang 4+5 formation of JiYuan area after detailed observation and description:The formation is mainly composed of fine grained feldspar sandstone colored by light-gray, gray-blue, brown-green, gray-white meanwhile debirs feldspar sandstone can often be found either because of the abundant debris and so does the feldspar quartz fine powder sandstone can be seen by accident. Due to surrounding intense volcanic activities of Yanchang stage, volcanic matters are major part of debris which can be identified under microscope.The pore structure is complex mainly made up by primary intergranular pore and dissolution pore of which throats seem like flake and tube and are small in diameter. As the typical low porosity/extra low permeability and ultra low permeability reservoir, the porosity of whole area has values mainly between 10% and 14% and also permeability is mainly between 0.01 md and 0.4 md.Compaction and cementation mainly decrease porosity while anti-compaction and dissolution are constructive to porosity. Chlorite film around the particles occupies pores and blocks throat turning out to be decreasing both porosity and permeability. By the analysis of electron probe, chlorite ingredients have Diabantite and penninite which formed under the temperature 120??180? during stage A-B of the Middle diagenesis.Based on the reservoir features above, the major factors influencing reservoir storage capacity can be considered to be sedimental facies, diagenesis and volcanic matter. Especially the existence of tuff material, make the pore structure of reservoir is good, but the distribution of the strong heterogeneity. |
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