Abstract
Aromatic hydrocarbons (AHc), as major constituents of coal and petroleum systems, are widely used as geochemical proxies for depositional environment, organic matter source, and thermal maturity. In this study, semi-open pyrolysis experiments were conducted on low-maturity humic organic matter (HOM) from the Ordos Basin. After fractionation of the liquid products, the aromatic fractions of retained oil (ReO) and expelled oil (ExO) were analyzed by gas chromatography–mass spectrometry (GC–MS), and 145 aromatic compounds from 16 homologous series were identified. Naphthalene, phenanthrene, dibenzothiophene (DBT), and pyrene series were selected to evaluate maturity parameters and to examine molecular processes relevant to late-stage gas generation. The results indicate that: (1) these aromatic series generally exhibit a unimodal abundance pattern during HOM maturation, with an initial increase followed by a decline, and the phenanthrene series remains dominant; (2) alkyl aromatic parameters can record thermal maturity within a defined window (Meas-Ro approximately 0.85–1.42%), among which alkyl phenanthrene parameters show the highest sensitivity, consistent with observations from sapropelic organic matter (SOM) and coal; and (3) the aromatic-rich framework of HOM favors the formation of thermally stable pyrobitumen and may provide methyl-derived methane during late-stage gas generation. At Meas-Ro values above 1.42%, the abundances of naphthalene and phenanthrene decrease markedly, suggesting consumption during high-maturity transformation, although the contributions of non-hydrocarbons and asphaltenes require further investigation. This study supports the application of aromatic maturity parameters in humic-derived liquid hydrocarbons and provides new constraints on late-stage gas generation from HOM. The findings provide a geochemical basis for evaluating the gas-generation potential of coal-bearing source rocks and may contribute to the exploration of deep and ultra-deep coal-derived gas accumulations.
Paper Infromation:
Mingxiang Yang, Chaojin Lu, Zhen Qiu, Huayao Zou, Haohao Wang, Geyu Pang, Chenzhao Quan, Jiong Ling, Ziqi Feng*, 2026. Maturation of aromatic hydrocarbons derived from humic organic matter and significance in late-stage gas generation. Organic Geochemistry 221, 105276.
