Formation Rock Evolution And Compaction Mechanism Of Chang-7 Reservoir In The South Central Area Of Yishan Slope In Ordos Basin

In order to study the characteristics of diagenetic evolution and densification mechanism of Chang 7 reservoir group in Yanchang Formation of Yishan Slope,Ordos Basin,and to play a scientific role in the exploration of Ordos Basin in the future.Based on the lithological characteristics,structural characteristics,pore type and pore structure characteristics and diagenesis experiments of the reservoir,and according to the analysis and testing methods of conventional thin section,casting thin section and inclusion temperature measurement,this paper has an impact on the tight reservoir characteristics,compaction mechanism,diagenetic evolution characteristics and reservoir physical properties of Chang 7 oil reservoir group of Yanchang Formation in Ordos Basin.The main factors are systematically studied.The results show that the lithology of the tight sandstone reservoirs in Chang 7 reservoir group is mainly feldspathic lithic sandstone and lithic feldspathic sandstone with fine grain size and high content of plastic particles.The pore type is mainly secondary pore,and the pore structure is characterized by low porosity and low permeability.The diagenetic stages of reservoirs are mainly divided into two stages and five sub-stages,namely early diagenetic stage A and B,middle diagenetic stage A₁?sub?,A₂¹?sub?,A₂²?sub?and middle diagenetic stage B.With the gradual increase of burial depth,diagenesis is also increasing,which leads to the rapid increase of tight reservoirs in Chang 7 reservoir group in the middle diagenetic stage.The characteristics of sediments in tight reservoir of Chang 7 reservoir group are characterized by diagenetic tight reservoir.The main pore type is secondary pore,and the diagenetic stage is medium A₂².However,the grain size of the sediments is mainly siltstone and fine sandstone,which also conforms to the characteristics of sedimentary tight reservoir.Therefore,the dense genesis of the tight reservoir of Chang 7 reservoir group in the central and southern part of Yishan slope of Ordos Basin belongs to mixed genesis,but mainly diagenesis.In the study of reservoir physical properties,it is found that sedimentation,diagenesis and pore structure have a major impact on reservoir permeability,but have a low impact on porosity.