Diagenesis and diagenetic evolution of tidal flat facies clastic rocks of Sinian Sugetbrak Formation in Northwest Tarim Basin

A set of tidal flat facies deposits are developed in the Sugetbrak Formation in the northwest of the Tarim Basin, which is the main target of oil and gas exploration in this formation. Based on the geological survey of Shiairike, Qigebrak and Qiaoenbrak sections, the diagenesis and diagenetic evolution of marine clastic rocks are studied by means of thin section identification, cathodoluminescence, scanning electron microscope, fluid inclusion temperature measurement and clay mineral X-diffraction, so as to provide a geological basis for further oil and gas exploration deployment and reservoir prediction of the Sugetbrak Formation in the Tarim Basin. The results show that: (1) Sand bodies in tidal flat sedimentary environment are developed in the Sugetbrak Formation in the study area, the sandstones are mainly lithic quartz sandstone and lithic sandstone, and feldspathic lithic sandstone is occasionally seen, with medium compositional maturity and structural maturity; (2) The sandstone of the Sugetbrak Formation has experienced diagenesis such as compaction, cementation, dissolution and replacement. Compaction is the direct cause of reservoir densification, and calcareous and siliceous cementation are the fundamental factors of reservoir densification; (3) The diagenetic evolution stage of Sugetbrak sandstones has reached the middle diagenetic stage B. the diagenetic evolution sequence is: compaction / autogenous clay mineral (chlorite) rim - the first stage feldspar and rock debris dissolution - the first stage silica cementation - the first stage mud microcrystalline calcite cementation / pressure dissolution / illitization of clay minerals - the second stage silica cementation / the second stage iron calcite cementation - calcium cement dissolution. The diagenetic evolution model provides a reliable geological basis for the prediction of ultra-deep tight sandstone reservoirs in the Tarim Basin.