High-temperature GC evidence for the early formation of C₄₀₊ n-alkanes in coals

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• 作者：Killops ; Stephen D. ; Carlson ; Robert M.K. ; Peters ; Kenneth E.
• 关键词：Coal ; Cutan ; High-temperature GC ; Wax ; High-molecular-weight ; n-alkanes
• 刊名：Organic Geochemistry
• 出版年：2000
• 期刊代码：40_01466380
• 类别：pw
• 出版时间：June, 2000
• 卷：31
• 期：6
• 页码：589-597
• 文件大小：276 K

摘要

High-temperature GC analyses were performed on a coal-sourced waxy oil from the Toka-1 well in the Taranaki Basin and on three bitumens, extracted ultrasonically with boiling toluene, from coals from the Tara-1 well in the Great South Basin, New Zealand. The coals represent an evolutionary trend from immature to post oil expulsion. In all samples the C₄₀₊ alkanes were characterised by dominant straight-chain members up to about C₆₅, which decreased significantly in abundance in bitumen with increasing maturity. They are present at an early stage of maturity, prior to the main phase of n-alkane generation, and may be liberated from cutan/cutin sources within kerogen by thermal decarboxylation of esters or have an earlier origin in the bitumen inherited from diagenesis. An odd-over-even predominance in the C₄₀₊ n-alkanes was most marked in the C₅₁–C₅₇ range and decreased with increasing maturity, suggesting that minor amounts of C₄₀₊ n-alkanes with a CPI approaching 1 are also generated during catagenesis. However, the observed C₄₀₊ n-alkane distributions may be affected to a degree by decreasing efficiency of solvent extraction with increasing n-alkane molecular weight, and by further long-chain n-alkanes generated during catagenesis being partially inaccessible to solvent extraction.