Carbon isotopic characteristics of different genetic type condensates in China

Abstract

Condensate pools with reservoir ages of Ordovician, Permian, Triassic, Jurassic, Cretaceous, Eogene, and Neogene were found in every giant petroliferous Basin in China. Condensates generated by sapropelic organic matters (sapropelic condensates) are of high-to over-mature stages, while the maturities of those generated by humic organic matters (humic condensates) cover a wide range, from early mature to over-mature. Carbon isotopes of 143 condensate samples were analyzed in this work, and we found that both the organic matter type and the maturity significantly influenced the isotopic composition of the condensates. The total hydrocarbon isotopic values of the humic condensates range from-29.9% to-21.7%, with an average of-26.0% (94 samples), while those sapropelic condensates are lighter generally, covering a range of-33.9% to-26.0% with an average of-29.5% (40 samples). δ 13C aromatics value is strongly inheritable to the organic matter type and it combined with the δ 13C saturates value can be used to distinguish condensates of different types. δ 13C aromatics value of sapropelic condensate is less than-27.5%, while the δ 13C aromatics and the δ 13C saturates values of humic condensate are larger than-27.5% and-29.5%, respectively.