Diagenetic Evolution and Its Impact on Reservoir Quality of Tight Sandstones: A Case Study of the Triassic Chang-7 Member, Ordos Basin, Northwest China

The Upper Triassic Chang-7 Member of the Ordos Basin contains typical tight sandstone reservoirs. Reservoir quality is affected by diagenesis, which a critical factor in oil exploration. In this study, sandstones were studied variety experimental methods, including thin sections, scanning electron microscopy (SEM), and X-ray diffraction (XRD), to determine reservoir characteristics diagenesis discuss their influences on quality. are mainly lithic arkose feldspathic litharenite with an average porosity permeability 7.17% 0.13 mD, respectively. pore type primary intergranular pores, secondary pores feldspar dissolved relatively developed, radii 2–20 µm. Diagenesis reservoirs includes compaction, quartz cementation, carbonate clay mineral dissolution. diagenetic stage develops into Mesodiagenesis A. loss from compaction cementation 15.93% 18.67%, With increase burial depth, gradually decrease. mesodiagenesis, authigenic illite compacts reservoir. acid fluid carried two stages gas filling during cement, plays certain role transforming