Reservoir Diagenesis of Chang 6-8 in Yangchang Formation of Zhengning Area in Ordos Basin

Reservoir sandstone of chang 6 and chang 8 in Yanchang Formation of Zhengning area in Ordos basin is typical of low porosity and low permeability,which has the characteristics of fine grain size,low compositional maturity,poor roundness and sorting. Based on casting slice identification of sandstone,scanelectron microscope,X-ray diffraction,reflection of vitrinite and physical property,we studied diagenetic characteristics of Yanchang Formation chang 6 and chang 8,analyszed their effect on reservoir physical property,and determined diagenetic stage of reservoir sandstone. diagenetic stage of reservoir sandstone is mainly the late diagenetic phase A. Our study shows that mechanical compaction and late cement of carbonate are the main factor causing the loss of porosity and reducing the reservoir quality of the sandstones.