| In this paper,the organic matter abundance,types and thermal evolution of the Permian Gufeng Formation,Dalong Formation,Longtan Formation and Silurian Gaojiabian Formation shale samples in the Lower Yangtze Region are systematically analyzed by various petroleum geochemical analysis methods.The Silurian Gaojiabian Formation shale in the Lower Yangtze Region is analyzed by elemental geochemical analysis and sedimentary source and sedimentary environment characteristics of the Shijiazhuang Gaojiabian Formation shale in the Lower Yangtze area were analyzed by elemental geochemical analysis techniques to investigate the shale gas geochemical conditions.The results show that these Paleozoic organic-rich shales in the lower Yangtze region have excellent petroleum geochemical characteristics and good shale gas generating conditions,which are mainly manifested in the following aspects:1.Organic matter is abundant and generally belongs to good-good source rock,which has a good material basis for shale gas generation.Among them,the Gufeng Formation in well DC1 belongs to good source rocks,while the Gaojiabian Formation belongs to good-good source rocks on the whole,and part of them belongs to poor source rocks.The Dalong Formation of Well HC1 belongs to good-good source rocks on the whole,Longtan Formation belongs to good-good source rocks,Gufeng Formation belongs to good-good source rocks and excellent source rocks are distributed on the whole,which belongs to good source rocks.Well HY1 Gufeng Formation belongs to good-excellent source rocks;Qixia Formation belongs to general source rocks;Dalong Formation belongs to excellent source rocks.In horizon,the organic matter abundance of Gufeng Formation is the highest,followed by Dalong Formation,Longtan Formation and Gaojiabian Formation,and Qixia Formation is the worst.2.The type of organic matter is good,which is consistent with the main shale gas horizons in the middle and upper Yangtze region.The organic matter in the three wells is mainly sapropelic.Among them,the sapropelic group of Gufeng Formation and Gaojiabian Formation in well DC1 has the highest component content and the best organic matter type,with type I kerogen as the dominant source rock;followed by Dalong Formation,Gufeng Formation and Gufeng Formation in well HC1,with better organic matter type and type Ⅱ kerogen as the dominant source rock;finally,Longtan Formation and Dalong Formation in well HY1,with better organic matter type,with type Ⅱ kerogen as the dominant source rock.Mainly.3.The vitrinite reflectance ranges from 1.2%to 2.3%,which is in the optimum thermal evolution stage for shale gas generation.The maturity of source rock samples of Gufeng Formation,Gaojiabian Formation,Dalong Formation and Longtan Formation in DC1,HC1 and HY1 wells is relatively high,which belongs to the maturity-high maturity thermal evolution stage.4.Source input of source rocks is mainly from low-grade aquatic organisms such as bacteria or algae,and a small amount of terrestrial higher plants,which ensures good hydrocarbon generation ability of sedimentary organic matter.Sedimentary geochemistry:P205 content,A1203 content and CaO content in Gaojiabian Formation are proportional to TOC;Cu,Ni,Sr and U elements are enriched,while Ba and Th elements are depleted;light rare earth elements are relatively enriched,while heavy rare earth elements are relatively depleted.5.Source rocks are deposited in deep water reduction environment,and sedimentary organic matter is effectively preserved.Among them,the sedimentary paleoclimatic conditions of Gaojiabian Formation are humid-thermal environment,the paleosalinity of water body is saltwater deposition,the oxidation-reduction environment of deposition is anaerobic reduction environment,and the paleo-water depth of deposition is deepwater deposition.These sedimentary conditions make the mudstone of Gaojiabian Formation become high-quality hydrocarbon source rock,which can be used as the main target of shale gas exploration. |
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