Diagenesis And Quantitative Pore Evolution Of Chang 8 Reservoir Group In Zhenjing Area Of Ordos Basin

The Yanchang Formation of the Upper Triassic in the southern part of the Ordos is the main oil production position. However, the oil layer of Yanchang Formation has the characteristics of low porosity and low permeability and ultra-low porosity and low permeability, which makes the oil and gas reservoirs more subtle and low yield, which makes the difficulty of oil and gas exploration and development improved. The diagenetic effect directly affects the microporous structure of the reservoir, which directly determines the porosity and permeability of the reservoir sandstone. Therefore, based on the study of the diagenesis of the reservoir in the Yanchang Formation, the factors that cause the low porosity and low permeability of the reservoir are found, and the reservoir physical evolution is analyzed quantitatively to achieve a good understanding of the reservoir.The Zhenjing Oilfield is located in the southwest margin of the basin,with gentle structure, simple structure and local development of small-scale nasal uplift, which provides favorable conditions for the relative enrichment of oil and gas. The study of the Chang 8 reservoir group lithology is silt- fine sandstone and mudstone interbed. The sedimentary facies are the delta facies underwater distributary channel microfacies and the underwater distributary bay microfacies. The thickness of the sand bodies is large, the distribution range is large, the physical properties are relatively good, and the main reservoirs in Zhenjing area are formed.The petrological characteristics and diagenesis of the Chang 8 reservoir group were studied by means of casting thin film analysis, X -ray diffraction analysis, electron microscopy, inclusion analysis and particle size analysis. Some conclusions were drawn. (1) The study area Chang 8 reservoir group is mainly composed of fine sandstone, and the medium - good and secondary prismatic rounds are composed of feldspar and high cuttings. The rock is named feldspar lithic sandstone and lithic Feldspar sandstone. (2) It is concluded that the main diagenesis of reservoirs in the study area is compaction, pressure dissolving,cementation, dissolution and metasomatism. According to various diagenetic phenomena, the diagenetic sequence is concluded and the reservoir diagenetic stage in the study area is in the middle of diagenetic stage. (3) In the study area, the chlorite membrane-calcite cementite phase, the feldspar-turbidite dissolution phase zone, the muddy interstitial phase zone, the feldspar dissolution zone and the kaolinite phase And the diagenetic facies are studied in five diagenetic facies.The porosity is dominated by intergranular pores with porosity of about 10.1%. Through the pores, throat of the reservoir pore structure analysis. The factors controlling the permeability of the reservoir are discussed from the aspects of sedimentation, diagenesis and tectonics.The initial porosity of the reservoir is restored by the calculation of the sorting coefficient, and the series of diagenesis processes, which are reduced by the compaction, the improvement of the dissolution effect and the cementation, are made in the diagenetic reservoir On the basis of lithofacies classification, the evolution curves of reservoir porosity in each diagenetic facies can be made.