Cross-stratigraphic Hydrocarbon Adjustment Controlled by Fluid Inclusions: A Case Study of the Santa Mu Area, Northern Tarim Uplift

The Santamu area, located in the Tabei Uplift of the Tarim Basin, is characterized by multi-stratigraphic accumulation and multi-stage charging. Integrating fluid inclusion petrography and microthermometry, in-situ U-Pb dating of calcite veins, and 1D burial history modeling, this study systematically reveals the cross-stratigraphic hydrocarbon adjustment processes and differential accumulation mechanisms within the Ordovician, Carboniferous, and Triassic reservoirs. The charging histories are precisely constrained: the Ordovician experienced three oil-charging phases (Late Caledonian–Early Hercynian, Late Hercynian, and Yanshanian) and one late gas charge, with the Late Hercynian being dominant; the Carboniferous and Triassic T3 subunits received oil during the Yanshanian and Himalayan periods, followed by gas; while the Triassic T1 subunit records only a single Himalayan oil charge. Critically, the study elucidates that the hydrocarbons in the Carboniferous and Triassic strata are not directly sourced from coeval Ordovician oils, but are products of vertical transfer and mixing. Specifically, early-charged (pre-Yanshanian) Ordovician hydrocarbons migrated upward along faults during the Yanshanian and Himalayan periods, with the T1 oil specifically derived from the vertical spillage of hydrocarbons originally trapped in the T3 subunit. The multi-stage differential activity of the NEE-trending strike-slip and Santa Mu fault systems is identified as the key controlling factor, where the opening, activity, and sealing of these faults dictated the vertical migration pathways, charging timing, and final accumulation. Consequently, a composite accumulation model is established for the area, characterized by "multi-stage generation from the Cambrian Yuertusi source rocks, fault-controlled migration, and cross-stratigraphic vertical adjustment," which deepens the understanding of hydrocarbon enrichment in complex cratonic fault zones and provides critical guidance for exploration in analogous regions.