Hydrocarbon Origin and Differential Accumulation Processes in the Dibei Area, Kuqa Foreland Basin

The Dibei area in the northern Kuqa foreland basin is an important target for hydrocarbon exploration in deep tight sandstone reservoirs. The anticline and slope belts in Dibei area record markedly different hydrocarbon properties and accumulation histories, and the origin of this contrast remains unclear. We integrated oil and gas geochemistry, fluid inclusion petrography and microthermometry, and burial and thermal history modeling to reconstruct hydrocarbon charging in the Jurassic Ahe Formation. The integrated geochemical data are consistent with qualitative contributions from Triassic lacustrine and Jurassic coal-measure source rocks to the reservoir oils, although their relative contributions cannot be reliably quantified. Molecular and carbon-isotope data indicate a predominantly coal-derived origin for the natural gas, with the Yangxia Formation considered the most plausible principal source. The anticline belt records two episodes of oil charging at approximately 21 and 15 Ma, represented by oil inclusions with yellow-green and blue fluorescence, respectively, followed by gas charging at approximately 6 Ma. In contrast, the slope belt preserves only the later oil charge at approximately 15 Ma and subsequent gas charging at approximately 9 Ma. These differences attributed to the timing of source rock maturation, fault activity, and effective trap development. Mature source rocks and early trap formation provided favorable conditions for early oil accumulation in the anticline belt. Subsequent fault activity enhanced connectivity between source rocks and reservoirs, enabling later oil charging in both belts. Gas invasion and renewed fault activity then modified and redistributed the earlier oil accumulations. These findings provide a representative example for understanding differential hydrocarbon accumulation in tight sandstone reservoirs of foreland basins.