Evaluation of Hydrocarbon Generation Potential and Geochemical Characteristics of Aromatic Hydrocarbons in Carboniferous–Permian Coal-Measure Source Rocks of Marine–Continental Transitional Facies in Fuyang Sag, Southern North China Basin

C values (-26.47‰ to -17.15‰) indicate predominantly Type III organic matter. Combined with the total thickness and single-layer thickness of effective source rocks in different layers, the quality of source rocks in the Shanxi Formation is slightly better. The overall thickness of effective source rocks in the Shihezi Formation is comparable to that of the Shanxi Formation. Still, frequent changes in sedimentary facies result in dispersed, discontinuous, high-quality layers. Consequently, the Shanxi Formation contains slightly better source rocks than the Shihezi Formation, with the Taiyuan Formation being the poorest. In summary, the hydrocarbon generation potential of the Carboniferous-Permian coal-bearing source rocks in the marine-continental transitional facies of the Fuyang Sag is generally low, and oil is the primary source. Effective hydrocarbon source rocks are characterized by thin thicknesses and a discontinuous distribution, which make it difficult to develop adequate hydrocarbon expulsion capacity and large-scale oil and gas accumulation. This explains the root cause of the low gas measurement value and the lack of a good oil and gas display in WFD-1 from a geochemical perspective.