Geochemistry and Hydrocarbon Generation of Coal Measures in the Daji Region, the Southeastern Margin of the Ordos Basin

Deep coal measure gas (DCMG) is regarded as a crucial strategic low‐carbon energy resource that plays a significant role in increasing national gas reserves; however, its formation mechanism under deep and complex geological conditions remains controversial. Using Rock‐Eval, stable‐isotope geochemistry, high‐resolution transmission electron microscope (HRTEM), Raman spectroscopy and basin modelling, this study deciphers DCMG generation and enrichment in coal measure from the Daji region, eastern Ordos Basin. Results demonstrate that the coal measure samples fall within the dry gas window, exhibiting vitrinite reflectance ( R o ) values between 1.87% and 2.67%. HRTEM imaging and Raman spectra document a systematic increase in aromatic‐ring condensation and incipient graphitisation with advancing thermal maturity. Kerogen δ 13 C and δ 15 N values covary positively with R o , reflecting isotopic fractionation during hydrocarbon expulsion. Thermal modelling indicates that a Yanshanian magmatic pulse elevated basal heat flow to ~125 mW/m 2 , accelerating organic‐matter maturation and driving peak DCMG generation at ~168 Ma. We propose a three‐stage tectonic‐controlled enrichment model: (a) magmatic overpressure established a free‐gas‐dominated system; (b) Late Cretaceous–Paleogene uplift opened fracture corridors that facilitated eastward gas loss; and (c) subsequent biogenic recharge partially replenished the reservoir. The findings provide a quantitative tectono‐thermal framework for predicting DCMG sweet spots in analogous deep basins worldwide.