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Abstract: Pyrolysis was carried out in anhydrous closed system (gold tubes) under a constant pressure of 50MPa to discuss the differences of gas generation mechanism between crude oil and its asphaltenes. Yields and carbon isotopic composition of gaseous hydrocarbons were determined. The results show that the yield curves of gaseous hydrocarbons generated from crude oil have analogy change trends with that of asphaltenes correspondingly. The yield of methane generated from asphaltene cracking is 50% of that of oil cracking when oil and asphaltene cracked completely. The relation of δ 13C1 < δ 13C2 < δ 13C3 exists in the whole process of pyrolysis, and the δ 13C value of methane, ethane and propane generated from oil is more than that of asphaltene correspondingly. Kinetic parameters of gaseous hydrocarbon generation for crude oil and asphaltene were obtained by kinetic calculation, and the result can be extrapolated to geological conditions. [Copyright &y& Elsevier]

Mild oxidative degradation was used to release the aliphatic hydrocarbons occluded inside the macromolecular structure of solid bitumens collected from Sinian carbonate reservoir, Sichuan basin, SW China. In contrast to the adsorbed aliphatic hydrocarbons extracted from the solid bitumens, the mild oxidative products showed unaltered n -alkanes distributions, which had been trapped within the macromolecular structure of the bitumens and protected from biodegradation processes. These observations are quite informative and suggest that at least, two phases of hydrocarbon charging to the Sinian reservoirs might have occurred. The occluded hydrocarbons seem to represent the first phase of hydrocarbon charge while the adsorbed and biodegraded hydrocarbons correspond to the second phase of hydrocarbon charge. However, terpane and sterane distributions in both fractions were preserved and similar, and the carbon isotope analysis results obtained in this work along with the previous geological information, corroborates the idea that Sinian reservoirs hydrocarbons have been sourced from the black shale of Lower Cambrian Qiongzhusi Formation. This study reveals the geochemical significance of adsorbed/occluded aliphatic hydrocarbons in understanding the charging history of oil into reservoirs. [ABSTRACT FROM AUTHOR]