Geochemical characterization of an oil seep from the Bagua Basin, north-central Peru

详细信息    查看全文

• 作者：T. Gentzis ; ^{thomas.gentzis@corelab.com}
• 关键词：Peru ; Bagua Basin ; Oil seep ; Biomarker geochemistry
• 刊名：International Journal of Coal Geology
• 出版年：2013
• 出版时间：30 March, 2013
• 年：2013
• 卷：108
• 期：Complete
• 页码：18-26
• 全文大小：2035 K

文摘

Oil hosted in a rock taken from a seep exposed by a road cut in north-central Peru was studied by geochemical means. The oil is classified as heavy paraffinic (waxy) by liquid chromatography. The oil appears to be highly mature, showing evidence of chemical and/or biological degradation. This is further supported by relatively high yields of polar fractions (resins and asphaltenes), partial depletion of n-alkanes below C₁₆, and a relative enrichment of isoprenoid hydrocarbons. The n-alkane distribution obtained by whole-oil gas chromatography (GC) also points to mature, waxy oil. Pristane/phytane and isoprenoid ratios suggest that Type II kerogen deposited in low-oxygen (dystrophic) environment was likely the source of the oil. Biomarker fingerprints of the saturate fraction obtained by gas chromatography-mass spectrometry (GC-MS) and other characteristic ratios indicate the high level of thermal maturation of the oil and suggest that the oil was derived from a clay-rich source rock rich in bacterial-derived organic matter deposited in suboxic conditions. Aromatic biomarker data confirm the high level of thermal maturity of the oil and point to a mixed shale/carbonate source rock deposited in a sulfate-poor marine environment. The parent oil most likely has a pre-Cretaceous source due to the absence of 18 ¦Á (H) oleanane and the fact that the C₂₈ ¦Á¦Â¦Â/C₂₉ ¦Á¦Â¦Â steranes and the C₂₈ ¦Á¦Â¦Â/C₂₉ ¦Á¦Â¦Â sterane vs. C₂₇ ¦Á¦Â¦Â/C₂₉ ¦Á¦Â¦Â sterane ratios are both comparable to values reported for oils derived from the Jurassic Pucara Formation source rock in the nearby Mara?on Basin.