| Petroleum asphaltenes was defined as macromolecules which can be dissolved in benzene or toluene but not soluble in low molecular alkanes. Petroleum asphaltenes have been widely used in many areas of geochemical studies, such as oil/source and oil/oil correlations, tracing the source of studied samples, maturity of petroleum and the temperature of oil formation. Tarim basin is a typical compositional basin in China, and Lunnan oil field is the most complicated area of Tarim basin due to its diversity of oil chemical and physical properties. It was difficult to carry oil/oil or oil/source correlations with low molecular compounds, and the source of oils from Lunnan area is still a question in debate.In this work, the molecular structure of petroleum asphaltenes from Lunnan area was determined by pyrolysis-gas chromatrography-mass spectrometer(Py-GC-MS), methylation-Py-GC-MS and Ruthenium Ion Catalyzed Oxidation(RICO). Moreover, the structure of petroleum asphaltenes, asphaltenes from Silurian oil sandstones and kerogens from source rocks, Tarim basin, were analysed by Py-GC-MS. Based on these results, the source of oils from Lunnan area were discussed with a point of view of structure of macromolecules and sedimentary environments.1.It was found that the elemental compositions, isotopic compositions and the molecular structure of asphaltenes precipitated from oil didn't change under different conditions in the precipitation experimnet. The pyrolysate of asphaltenes can be used as the substituent of low molecular compounds for oil-source rock correlation and also for identification of oil source whatever the oil reservior in superposed basin was charged by secondary gas or condensate oil.2. The molecular structure of oil asphaltenes from Lunan area of Tarim basin was elucidated by flash pyrolysis, methylation-pyrolysis and RICO. The substituted functions in oil asphaltenes from Lunan area were dominated by n-alkyl side chains. H-Alkyl bridges and minor alkyl cyclohexanes, branched alkanes and alkyl benzenes were also identified. These functions maybe were linked to the structure of asphaltenes by C-C bonds. The aromatic ring systems of oil asphaltenes were mainly composed of naphthalene and phenanthrene and seldom of highly condensed aromatic rings.3.The pyrolysates of oil asphaltenes from different tectonic belt, reservoirs, and different kinds of oils from Lunnan area were similar, which suggested these oils were generated from sources under the same sedimentary environment. Moreover, The pyrolysates of asphaltenes extracted from Silurian oil sandstones of Tabei and Tazhong area, Tarim basin, also exhibited similar characteristics to that of petroleum aspaltenes from Lunnan area. A most striking feature of the pyrolysates was identification of high abundance of 1,2,3,4-tetramethyl benzene and minor amounts of aromatic isoprenoids. The 1,2,3,4-tetramethyl benzene of pyrolysates from closed system pyrolysis of asphaltenes from oils and Silurian oil sandstones show very heavy carbon isotopic compositions, and the 1,2,3,4-tetramethyl benzene was enriched in 13C by more than 10%o compared with the normal alkanes in pyrolysates. This results unambiguously proved that high1,2,3,4-tetramethyl benzene in asphaltenes from oils and Silurian oil sandstones was from green sulfur bacterial, and the source of Lunnan oils and Silurian oil sandstones was derived from an stratified water column under strong reducing conditions. 4. The molecular structure of kerogens from source rocks, Tarim basin, were also studied by Py-GC-MS and methylation-Py-GC-MS, and the depositional enviroment of Cambrian and Ordovician source rocks was compared based on the geochemical characteristics of extracts from these two sets of source rocks. 1,2,3,4-tetramethyl benzene and l-alkyl-2,3,6-trimethyl benzenes were both detected from extracts of Cambrian and Ordovician source rocks. However, the abundance of l-alkyl-2,3,6-trimethyl benzenes from extracts of Cambrian source rocks from Fang 1 and Tadong 2 wells was much hi...
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