Late-Stage Hydrocarbon Generation in Overmature Coal-Measure Source Rocks of the Southern Ordos Basin

The Permian Taiyuan and Shanxi Formations of the Upper Paleozoic in the Ordos Basin are the primary source rock sequences for tight sandstone gas. The core problem lies in the uncertainty surrounding the gas generation process at the overmature stage. To clarify hydrocarbon generation processes and the potential of coal, carbonaceous mudstone and dark mudstone, we integrate basin modeling and hydrocarbon generation pyrolysis thermal simulation experiments. Using PetroMod software and measured well data on vitrinite reflectance (Ro), total organic carbon (TOC), Tmax and hydrocarbon generation potential (S1 + S2), we quantitatively reconstruct the burial, thermal, maturity and hydrocarbon evolution histories of the southern Ordos Basin. The results indicate that the main oil generation window is concentrated at 400 °C, and gas yield increases continuously from 350 °C to 700 °C without a peak, showing that coal and carbonaceous mudstone still have considerable hydrocarbon generation potential under extreme high-temperature conditions. Combining the hydrocarbon generation ratio, rock density and TOC data, coal is identified as the predominant source rock in the southern Ordos Basin. This study provides a scientific basis for tight gas exploration in cratonic basins, enhances the understanding of gas generation in coal-bearing source rocks, and offers a new perspective for oil and gas resource evaluation.