Evaluation and biogenetic derivation and sedimentary environment of source rocks from Permian in the Lower Yangze region

Based on drilling cores and outcrop samples of the land and ocean area in lower Yangtze region as the research object, by using the research methods of organic petrology and organic geochemistry, reveal the vertical and planar organic geochemical characteristics, hydrocarbon potential, biogenetic derivation and sedimentary environment of four groups of Permian source rocks in the Lower Yangtze region, i.e.the Upper Permian Dalong Formation and Longtan Formation, Lower Permian Qixia Formation and Gufeng Formation.According to the results of the experiment test, combining previous research data, comprehensive analysis shows that the organic matter abundance of the source rocks of Qixia Formation and Dalong Formation are medium-good level, the source rocks of Longtan Formation belong to fair-medium level, the source rocks of Gufeng Formation achieve very good level.Judging from the organic matter abundance, the Lower Permian source rocks which in the Lower Yangtze ocean area are better than in the land area of which, while the Upper Permian source rocks are opposite feature.According to the characteristics of the carbon isotopes, the source rocks of Lower Permian Qixia Formation mainly constitute Type Ⅰ-Ⅱ kerogen and the other three groups of source rocks are Type Ⅱ-Ⅲ kerogen.Four groups of Permian source rocks have vitrinite reflectance values ranging mostly from 1.3% to 2.0%, suggesting a high-mature level with regard to hydrocarbon-generating.The results show obvious inhomogeneity in the spatial distribution of mature.Four groups of Permian source rocks have slimilar sterane and terpane characteristics, which biological sources mainly came from low aquatic organisms.Four groups of source rocks were setting in the weak reduction environment to weak oxidation environment, of which depositional environment is turbulent and biological change is obvious in the Dalong Formation.In summary, the Permian source rocks have high organic abundance and good types of organic matter, and provide the material basement for forming large oil and gas fields in the Lower Yangtze region.In particular, the Gufeng Formation source rocks, which have been neglected in the past, are a set of potential high-quality source rocks, which have important guiding significance for further oil and gas exploration in this area.