Tar-rich coal with extractable oil and gas through low-temperature pyrolysis is widely distributed in the Santanghu Basin, Xinjiang. However, there were significant differences in the tar yield of tar-rich coal at different sedimentary horizons, which constrained detailed exploration and evaluation. This paper investigates coal samples from the Badaowan and Xishanyao Formations in the Santanghu Basin, integrating macro sedimentary evolution, tar yield analysis, sedimentary facies identification, coal facies classification, and microscopic molecular structural characterization. The objective is to elucidate the relationships among these parameters, clarify the sedimentary environment's control mechanism on tar yield, and establish a systematic framework linking the sedimentary environment, coal maceral, and hydrogen-rich structures to tar generation.
The Badaowan Formation coals, deposited in a lowland moor environment in the Interdistrbutary bay of the Lower Delta Plain facies, exhibit distinct characteristics. These settings were characterized by stable, deep overlying water and intense gelification, fostering the formation of coals with high vitrinite content. In contrast, the Xishanyao Formation coals formed in a high moor environment along the shallow lake shore facies, where shallow water and periodic peat exposure promoted oxidation, resulting in elevated inertinite content.
The molecular structure of Badaowan Formation and Xishanyao Formation coal was analyzed by Fourier transform infrared spectroscopy (FTIR) and ¹³C nuclear magnetic resonance (13C-NMR). Badaowan coals contain higher aliphatic hydrogen structures, particularly methylene and methyl, with longer aliphatic chains than Xishanyao coals. Conversely, Xishanyao coals are dominated by aromatic hydrogen structures and exhibit higher oxygen-containing functional groups. Aliphatic chain structures, particularly methylene and polymethylene structures, are identified as critical molecular structural for tar formation in tar-rich coals.
Coals deposited in deeper, more reducing peat swamps with stable water columns and intense plant tissue degradation accumulate abundant aliphatic hydrogen structures, leading to higher tar yields. The Badaowan Formation coal has the above characteristics of key substances and a coal-forming environment, resulting in a higher tar yield than the Xishanyao Formation coal. In additional, the response of plant types and paleo-geothermal metamorphism at different coal-forming periods to tar yield requires further investigation.
谷歌
火狐
