Elevated Mango’s K1 Values Resulting from Thermochemical Sulfate Reduction within the Tazhong Oils, Tarim Basin

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• 作者：Daofu SongChunming Zhang ; Sumei Li ; T.-G. Wang ; Meijun Li
• 刊名：Energy & Fuels
• 出版年：2017
• 出版时间：February 16, 2017
• 年：2017
• 卷：31
• 期：2
• 页码：1250-1258
• 全文大小：500K
• ISSN：1520-5029

文摘

Mango proposed a significant invariance of four isoheptanes, in which a ratio of sums (K₁) remains at approximately 1, regardless of the absolute concentrations. Gas chromatographic analyses of 70 oils from the Tarim Basin demonstrated that most of these oils share invariant K₁ values close to 1.0, even if they are derived from different sources and have varying degrees of maturity and biodegradation. However, a few unexpectedly high K₁ values occurred in certain oils from the Tazhong-4 Oilfield in the Tazhong Uplift, and these oils are characterized by abnormally high contents of dibenzothiophenes (DBTs). An excellent positive correlation between the elevated K₁ values and the abnormally high DBT contents indicated that the thermochemical sulfate reduction (TSR) alteration, which contributed to the increased DBT contents, likely resulted in the elevated K₁ values. Methylhexanes (MHs) are assumed to be more susceptible to TSR than dimethylpentanes (DMPs), and the terminal methyl groups of C₇ compounds are more resistant than their mid-chain isomers in the TSR-altered oils. Therefore, in the oils affected by TSR alteration, a decrease in the 2,3-DMP/2,4-DMP ratios will not be sufficient to offset the increased 2-MH/3-MH ratios, which results in elevated K₁ values. A positive correlation between the increased 2-MH/3-MH ratios and the elevated K₁ values has validated this hypothesis.