The Diagenetic Characteristics And Its Influence On The Reservoir Property Of Chang 4+5 In The Ji Yuan Area Of Ordos Basin

The study on the influence of diagenesis on the evolution of reservoir and its controlled mechanism can provide a research basis for the effective prediction of reservoir.The Chang 4 + 5 in Jiyuan area belongs to tight sandstone reservoir because of the characteristics of strong heterogeneity,small granularity,lots of complicated diagenesis types,complex pore structure and showing low permeability and low porosity.But the reservoir capability is good,having good oil flow display status,so the study on the characteristics of diagenesis in the study area and its effect on reservoir property has a certain reference value of late exploration and development in this area.By polarizing microscope,scanning electron microscope observation methods,combined with the existing research results in study area,The paper analyzes the characteristics of the pore types and structure,research the characteristics of diagenesis,ascertain the diagenetic stage,reach its influence on reservoir property in the study area,and finally obtain the following harvest and understanding:(1)The characteristics of low quartz,high feldspar and high mica are common in the whole study area,but the unstable and soluble sandstone in the northeast area is more than that in the west.High content feldspar is the material basis of large scale dissolution of feldspar in late stage.(2)The diagenesis method is varied and complex,including a series of constructive diagenesis,such as dissolution,metasomatism and rupturing,as well as some diagenesis being destructive on reservoir quality: compaction,pressure solution and cementation.(3)After mading a systematic diagenesis study,the paper found that the study area in the early diagenetic exists alkaline diagenetic,such as diagenetic signs :quartz dissolution,calcite metasomatism quartz,calcite precipitation,feldspar secondary enlargement,and chlorite films;in the late stage of early diagenesis,there are mainly feldspar dissolution,kaolinite precipitation,quartz secondary enlargement,calcite dissolution and other diagenetic phenomena.And on the basis of authigenic mineral distribution characteristics,the combination between authigenic mineral,and ratio of illite-smectite(I/S),the paper judged that the Chang 4+5 reservoir in Jiyuan area is in the diagenetic stage of early diagenetic B to intermediate diagenetic A.(4)According to diagenesis and pore types,purpose reservoir facies in the study area can be divided into four categories: kaolinite cementation-feldspar corrosionsecondary dissolution pore phase,compaction resistance-chlorite film-residual intergranular pore phase,silicious / carbonate cementation-residual intergranular pore phase,carbonate cementation-dense phase.The first two has great contribution in the aspect of improving reservoir property.