Research on Diagenetic Facies of Low Permeability Reservoir: A Case Study of the Yanchang Formation in Longdong Area, Ordos Basin

Based on data of cast thin section, cathode luminescence and scanning electron microscope, the present paper comprehensively investigated the types and quantitative intensity of reservoir diagenesis of the Upper Triassic Yanchang Formation in Longdong area of Ordos Basin, distinguished the types of diagenetic facies from the aspect of quantitative index. The intensity calculation and classification of compaction, cementation and dissolution indicates that the Yanchang Formation of Longdong area experienced strong compaction including medium to strong compaction and extremely strong compaction locally for the high contents of matrix. There is great difference in cementation intensity which presents mainly in weak cementation with local medium to strong cementation. Dissolution is strong in study area mainly in medium to strong. The reservoir could be divided into eight types of diagenetic facies, including medium compaction with strong dissolution face, medium compaction with medium dissolution face, medium compaction with medium cementation and medium dissolution face, strong compaction with strong dissolution face, strong compaction with medium dissolution face, medium compaction with strong cementation face, strong compaction with strong cementation face and extremely strong compaction face. The reservoir quality of different diagenetic facies has a significant difference.