关键词: 海拉尔盆地, 南屯组, 页岩油, 富集规律, 甜点评价

Abstract: Well W64, a key preliminary prospecting well in Hailar Basin, was completed and tested for oil in 2025, yielding a high commercial oil flow of 16.2.t/d. This result marks a major breakthrough in the shale oil exploration of Nantun Formation within the oil-rich faulted depression zone of the central basin. Based on core, logging, mud logging, and experimental data from Well W64 and multiple legacy wells, the geological characteristics and principal controlling factors of shale oil enrichment and high productivity in Nantun Formation of Wuerxun-Beier sags were systematically investigated. The results indicate that three shale lithofacies are developed in the Nantun Formation of Wuerxun-Beier sags, i.e., laminated mixed shale, laminated felsic shale, and massive felsic shale. Among them, laminated felsic shale is characterized by high organic carbon content, high free hydrocarbon content, and high brittleness, with an average total organic carbon content of 2.01%, an average free hydrocarbon content of 4.8.mg/g, and an average brittleness index of 53.13%, making it a favorable exploration target for shale oil. The light, low-viscosity fluid characteristics and overpressure-coupled driving forces constitute the core mechanisms underlying high and stable shale oil production in Wuerxun-Beier sags. Shale oil in the Nantun Formation is characterized by low density and low viscosity. The measured crude oil density and viscosity in Well W64 are 0.806.1.g/cm³ at 20.℃ and 1.9.mPa·s at 50.℃, respectively. This outstanding fluid mobility effectively compensates for the relatively poor storage capacity of shale matrix pores. The weak to moderate overpressure system developed in the sag is spatially and temporally well matched with high-quality sweet spots, which not only facilitates the effective preservation of retained hydrocarbons but also provides sufficient driving energy for hydrocarbon production. Based on data from Well W64, a seven-property evaluation criterion for shale oil sweet spots was established, and four favorable shale oil exploration zones were identified in Wuerxun-Beier sags: southern Wuerxun subsag, western Beier subsag, northern Wuerxun subsag, and central Beier subsag. The total shale oil resource potential of these favorable areas is estimated at 2.12×10⁸t. The exploration breakthrough at Well W64 confirms the large-scale exploration and development potential of shale oil resources in Hailar Basin. It not only provides a new direction for increasing reserves and production in mature exploration areas of faulted basins within Daqing oilfield but also offers an important reference for shale oil exploration in similar medium- and small-sized faulted basins within the rift system of northeast China.

Key words: Hailar Basin, Nantun Formation, shale oil, enrichment regularity, sweet-spot evaluation