Characteristics of hydrocarbon source rocks in Amushan Formation in Manghanchaoke region of Alxa Right Banner, western Inner Mongolia

Based on a study of the lithologic association, vertical characteristics of sedimentary facies and regional sedimentary distribution of Amushan Formation in Manghanchaoke region, the authors hold that the flourishing period of Badanjilin marine rift basin was the sedimentary period of Amushan Formation, during which the shallow marine shelf facies mud shale of huge sedimentary thickness was deposited, which constitutes the main layer section of source rocks in this region. With TOC≥0.3% as the lower limit, the converted thickness of the source rock is 121.39m, in which the thickness of middle to higher organic carbon is 89.11m, possessing 58.9% of the thickness of the hydrocarbon source rock layer. A study of geochemical indexes of kerogen carbon isotopes, the relative content of C27 & C29 sterane and saturation hydrocarbon characteristics shows that the main kerogen type is Ⅱ type. An analysis of original sedimentary environment with Pr/Ph shows that the main sedimentary environment was a reducing environment, which was beneficial for the preservation of organic matter. And the characteristics of vitrinite reflectance solid, maximum pyrolytic temperature and illite crystallinity show that the source rock owed its conversion into higly-mature to over-mature stage and mainly over-mature stage to the influence of tectonic dynamic activity and magma metamorphism of late Variscan and Indo-Chinese epoch. There has been no regional metamorphism, so Amushan Formation is the main source rock layer section in this region.