Hydrocarbon Generation Processes of the Upper Carboniferous Coal in the Daning-Jixian Block, Eastern Ordos Basin: Insights From Geochemical and Three-Dimensional Basin Modeling

The hydrocarbon generation process of coal in coal-bearing basins is crucial for the comprehensive evaluation of natural gas resources. For the first time, the tectonic and thermal history of the upper carboniferous coal in the Daning-Jixian block, located at the eastern margin of the Ordos Basin, was systematically investigated using geochemical analysis and three-dimensional basin modeling. This study clarifies the genesis of coalbed methane, analyzes, and quantifies the hydrocarbon generation processes, generation intensity, and volume. Geochemical analyses demonstrate that the no. 8 coal seam exhibits total organic carbon content ranging from 47.3 to 73.3%, classifying it as a high-quality gas source rock dominated by Type III kerogen composition. Vitrinite reflectance measurements (Ro = 2.07–3.05%) indicate an overmature thermal evolutionary stage. The thickness of the no. 8 coal seam ranges from 0.9 to 9.8 m. Tectonic and thermal history analysis indicates that the coal experienced three burial stages: Stage I (360–250 Ma), Stage II (250–204 Ma), and Stage IV (140–120 Ma), as well as two uplift and denudation stages: Stage III (204–140 Ma) and Stage V (120–0 Ma). The hydrocarbon generation processes include two key episodes, occurring during Stage II and Stage IV. The total hydrocarbon generation intensity for no. 8 coal seam ranges from 2.23 to 32.04 × 108 m3/km2, with a cumulative hydrocarbon generation of 5.99 × 1012 m3. Gas composition and isotopic analysis show that the coalbed methane is primarily composed of high-maturity thermogenic gas, further validating the accuracy of the thermal simulation results.