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

Abstract

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.

Fluid inclusions and hydrocarbon accumulation stages of the Chang 73 sub-member in the Zhijing-Ansai area in the Ordos Basin

“…Some scholars suggest that there were two phases of accumulation in the Chang 7 member of the Ordos Basin, and that the main accumulation period occurred in the Middle-Late Early Cretaceous (Shi et al, 2012;Zhang et al, 2016;Qu et al, 2022). Some other scholars believe that there were three phases of accumulation in the Chang 7 member of the Ordos Basin, which occurred Middle-Late Jurassic to Early Cretaceous, Late Early Cretaceous, and Late Cretaceous (Guo et al, 2012;Fu et al, 2013;. The study area is located in the middle part of the Shanbei slope in the Ordos Basin.…”