Characteristics and sedimentary environment control of Jurassic tar-rich coal in Santanghu Basin
Tar-rich coal resources are widely distributed in Xinjiang region,from which oil and gas can be extracted through low-tem-perature pyrolysis.However,there is a great difference in the pyrolytic tar yield at different sedimentary locations,restricting the fine exploration and evaluation of tar-rich coal.This paper is a case study of coal samples extracted from Badaowan Formation and Xishanyao Formation in Santanghu Basin.Based on fully understanding of the aliphatic chain structure in the form of methylene and methyne as a key microscopic characteristic for tar-rich coals,the paper illustrates the molecular structural features of coal macerals and the effect of coal macerals on tar yield,and reveals the control law of peat bog environment on the coal molecular structure and tar yield.The results indicate that more long-chain aliphatic structures of vitrinites can help increase coal tar yield,and the tar-rich coal formed in the peat bog environment characterized by high water levels,strong reducing conditions and high-degree plant tissue degradation contains more aliphatic hydrogen structures,especially methylene and methyne structures,thus producing high-yield py-rolytic tar.The coal in Badaowan Formation processes the above characteristics of key substances and a coal-forming environment so that it has a higher tar yield than that in Xishanyao Formation.Meanwhile,plant types at different coal-forming stages and differ-ences in their responses to the thermal evolution of paleotemperature are also worth discussing.
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