Differential Hydrocarbon Expulsion Efficiency of Multiple Source Rocks in a Superimposed Basin: Evidence From the Southwestern Tarim Basin

ABSTRACT Quantifying the relative contributions of multiple source rock intervals remains a major challenge for petroleum exploration in superimposed basins. In the southwestern Tarim Basin (SWTB), the respective contributions of the Carboniferous, Permian and Jurassic source rocks have long been debated. This study integrates geological and geochemical data, burial‐thermal history reconstruction and hydrocarbon generation‐expulsion modelling based on the Hydrocarbon Generation Potential (HGP) method to quantitatively evaluate the hydrocarbon contributions of the three source rock intervals. The results reveal significant differences in expulsion efficiency. Carboniferous source rocks (Type II–III kerogen, average TOC 0.36%) generated 28.63 Gt of hydrocarbons and expelled 25.29 Gt, with an expulsion efficiency of 88.3%, accounting for 70.7% of total expelled hydrocarbons. Permian source rocks (Type II 2 –III kerogen, average TOC 1.3%) generated 27.47 Gt but expelled only 9.78 Gt (35.6% efficiency, 27.3% of total expulsion). Jurassic source rocks (Type II 2 –III kerogen, average TOC 2.19%) generated 8.09 Gt but expelled only 0.70 Gt (2.0% of total expulsion). The Carboniferous is therefore identified as the dominant contributor, the Permian as secondary and the Jurassic as minor. These differences are primarily controlled by organic matter type, thermal evolution history and reservoir‐caprock configuration. Hydrocarbon generation‐expulsion centres are concentrated in the Kashi Sag and the Kekeya‐Fusha area, where hydrocarbons migrated predominantly along strike‐slip fault systems, forming a near‐source vertical accumulation pattern. The results demonstrate that hydrocarbon contribution is controlled not only by hydrocarbon generation potential but also by hydrocarbon expulsion efficiency, providing a quantitative basis for identifying dominant source rocks and evaluating multi‐source petroleum systems in complex superimposed basins.