Kerogen carbon isotopic features and influencing factors of Carboniferous- Permian hydrocarbon source rocks in Ejina Banner and its vicinities, western Inner Mongolia, China

Many researchs indicate that the carbon isotopic composition of kerogen in hydrocarbon source rocks is mainly affected by kerogen types, and the composition can be used as an important evaluation index of hydrocarbon source rocks types, sedimentary environment and oil and gas source correlation. This method has been widely applied. Through the research of organic carbon abundance, geochemical characteristics, thermal evolution characteristics and carbon isotopic composition of kerogen in Carboniferous- Permian hydrocarbon source rocks of typical sections in Ejina Banner and its vicinities, it is showed that the Carboniferous- Permian hydrocarbon source rocks in the area are the mud rocks which formed in shallow marine shelf facies, and the source rocks have the characteristics of middle organic carbon, type II kerogen and mature-overmature evolution stage. The carbon isotopic composition of kerogen is remarkable heavier, and the distribution of carbon isotopic composition of kerogen is mainly affected by the thermal evolution and organic carbon abundance. The heavy carbon isotope is continuously concentrated, and the effects of carbon isotope is 4‰~6‰ during the mature-overmature stage. With the increase of organic carbon, the kerogen carbon isotopic composition is remarkable lighter, and the influence value can reach more than 4‰. Because the source rocks have already entered into the mature-overmature stage in this study area, the kerogen carbon isotopic had already been greatly changed. The effect of kerogen types is relatively reduced, so the kerogen carbon isotopic composition can not be used as the evaluation index of source rocks kerogen types.