Carbon Isotopic Compositions of Kerogen Chemical Degradation Products

Key words: 
• kerogen /
• selective chemical degradation /
• compoundspecific C isotopic composition /
• Songliao Basin

Abstract: A sequential selective chemical degradation was performed for the kerogen from the Nenjiang Formation of the southern Songliao Basin by using a series of mild chemical degradations. Subsequently, GCMS analyses were carried out for different degradation products. The results show that products of alkaline hydrolysis and desulfurization mainly comprise monocarboxylic acids and nalkanes. The carbon isotope curve of nalkanes displays a “negative sloping” (i.e. gradually depleted in 13C with increasing carbon number). Monocarboxylic acids, mainly including C16 and C18 acids, have an obvious even carbonnumbered predominance. Their carbon isotope compositions are similar to those of the corresponding nalkanes with same carbon number. Monocarboxylic acids and α, ωdicarboxylic acids are the dominant products of RuO4 oxidation. Carbon isotopic composition of monocarboxylic acids fall between －28.3% and －33.7‰, and a "negative sloping" is shown in the range of light carbon number, while a “positive sloping” in high carbon number part. δ13C values of α,ωdicarboxylic acid is similar to those of monocarboxylic acids in the range of light carbon number, indicating that they have the same source. The comparison shows that the nalkanes in the extracts from sample JL30 possibly have the mixing of other sources, and their carbon isotopic compositions present the mixing characteristics.