DIAGENESIS EVOLUTION OF TIGHT SANDSTONES IN CHANG 8 MEMBER OF UPPER TRIASSIC IN THE XIASIWAN AREA, ORDOS BASIN, CHINA

Diagenesis of tight sandstone reservoir controls pore evolution and influence the distribution of premium reservoir. The sandstones of Chang 8 Member in Xiasiwan area are typical tight reservoirs. Comprehensive analysis of adequate thin-sections, SEM data showed that the sandstone reservoirs underwent 4 types of diagenesis, including compaction, cementation, dissolution and replacement. Cementation is characterized by carbonate cement which can be divided into early and late stages. and dissolution is mainly about feldspar dissolution, being divided into early and late stages too. On the basis of analysis of the symbiotic association of diagenetic minerals and the homogenization temperature of fluid inclusions, the succession of diagenesis is divided: compaction - chlorite cementation, the first phase feldspar dissolution, kaolinite cementation - the first phase calcite cementation - quartz overgrowth - the second phase feldspar dissolution, the second phase calcite cement dissolution - the second phase calcite cementation, illite cementation. The reconstruction of diagenetic succession will provide guideline for the prediction of premium reservoir.