Diagenesis features of Chang 8 tight sandstone reservoir in Honghe Oil Field, Ordos Basin

The diagenesis types, distribution characteristics and main controlling factors of the tight sandstone reservoir in the 8th member of Triassic Yanchang Formation (Chang 8) in the Honghe Oil Field, Ordos Basin, were systematically studied by using thin sections, scanning electron microscopy and electron probe. The Chang 8 reservoir in the study area is currently in the middle A diagenesis stage. The diagenesis types related to the reservoir quality mainly include compaction, dissolution, calcite cementation, kaolinite cementation and chlorite cementation. The isolated thin layer sand body has a high plastic mineral content and was deposited in the channel flanks and upper reaches of the river. The diagenesis of this sandstone is characterized by strong compaction, weak dissolution and cementation, forming strongly compacted diagenetic facies. The stacked thick sand body was deposited in the center of the river. The top and bottom sand bodies are strongly cemented by calcite, while those in the central part developed multiple diagenetic sequences corresponding to different sandstone lithofacies types. The middle-fine sandstone lithofacies, rich in rigid minerals, includes chlorite cement, and the transitional fine sandstone lithofacies mainly contains kaolinite cement or middle calcite cement.