Accumulation Conditions and Models of Jurassic Tight Sandstone Reservoirs from a Coal-Measure Whole Petroleum System Perspective: A Case Study of the Sangonghe Formation, Taibei Sag, Turpan–Hami Basin, China

Abstract

Tight sandstone gas accounts for nearly 30% of China's natural gas production and is an important exploration target in western sedimentary basins. To clarify the accumulation mechanism of the Jurassic tight sandstones in the Taibei Sag, this study integrates sand-body characterisation, source-rock geochemistry, reservoir analysis, tectonic restoration, fluid-inclusion microthermometry, and burial–thermal history modeling within a coal-measure whole petroleum system framework. The Badaowan, Sangonghe, and Xishanyao formations contain three source-rock intervals composed mainly of coal and organic-rich mudstone. A progradational braided-river delta system deposited thick, laterally extensive sandstone bodies in the Sangonghe Formation, while a widespread mudstone at its top acts as a regional caprock. Reservoir space is dominated by dissolution and intercrystalline micropores, with porosity mainly ranging from 3% to 9% and permeability generally below 1 mD. Three hydrocarbon charging stages are identified: Late Jurassic (160–150 Ma), Early Cretaceous (143–100 Ma), and Late Cretaceous–present (67 Ma–present). Two temporal relationships between reservoir evolution and charging are recognised: concurrent densification and hydrocarbon charging, and hydrocarbon charging after densification. Hydrocarbon enrichment is jointly controlled by inherited paleostructural highs, fault-mediated migration, and effective reservoir sweet spots. The principal innovation is the temporal coupling of source–reservoir–caprock–fault configurations with reservoir densification and multiphase charging, which provides a more integrated explanation for tight-sandstone accumulation in Jurassic coal-measure successions.