Reservoir Forming Mechanism of the Yanchang Tight Sandstone in Honghe Oilfield, Ordos Basin.

Honghe oilfield is located in the southern Tianhuan Depression of the Ordos Basin. The Upper Triassic Yanchang Formation is in a normal or negative pressure state. The reservoir is tight with low permeability. The time relationship between reservoir densification and formation is very important in the dynamic mechanism analysis of hydrocarbon accumulation in tight sandstones. Combined with microfacies analysis of fluid inclusions, isotopic chronology of authigenic illite, numerical simulation of hydrocarbon generation evolution, and observation statistics under a microscope, this relationship is studied in the Yanchang Formation, and the reservoir forming mechanism of a tight sandstone under low dynamic background is analyzed. The results show that diagenesis and oil accumulation of the Yanchang Formation in the Honghe oilfield occur synergistically, and large-scale reservoir formation is earlier than the key densification event. The Yanchang Formation reservoir is the result of early filling, dominant channel, differential pressure driving, and other mechanisms under a low dynamic background, which shows the characteristics of early selective filling, late inherited filling, and disseminated expansion. The coupling evolution relationship between reservoir forming dynamics and resistance of different sandstones determines the differential accumulation and enrichment of strongly heterogeneous reservoirs. [ABSTRACT FROM AUTHOR]