Based on seismic,drilling,core,gas composition and isotope data,the characteristics of gas reservoirs in Leikoupo Formation of the middle Triassic of different structures in western Sichuan Basin are analyzed.Natural gas sources are classified,and the hydrocarbon accumulation model is clarified.The research shows that according to the difference of natural gas composition,the Leikoupo Formation gas reservoirs in western Sichuan Basin can be divided into two categories,namely,the piedmont concealed structural belt with slightly low alkane volume fraction,slightly high H2S and CO2 non-hydrocarbon volume fraction,and the piedmont depression zone with slightly high alkane volume fraction and slightly low H2S and CO2 non-hydrocarbon volume fraction.According to the difference of natural gas alkane isotope characteristics,the piedmont concealed structural belt can be divided into the structure of Shiyangzhen and Yazihe with lighter 813C2 and isotopes in reverse order,and Jinma structure with heavier δ13C2 and positive isotope distribution.The piedmont depression zone can be divided into Xinchang structure with lighter δ13C2 and isotope positive distribution,and Yongxing and Majing structures with heavier δ13C2 and positive isotope distribution.Based on the analysis of natural gas migration conditions and accumulation models,it is believed that the natural gas in Shiyangzhen and Yazihe structures comes from the source rocks of Longtan Formation and Leikoupo Formation.The natural gas of Jinma and Majing structures comes from the source rocks of Longtan Formation,Leikoupo Formation and Maantang Formation.The natural gas of Xinchang structure mainly comes from the source rocks of Leikoupo Formation,and some parts of the top structure have the limestone of the first Member of Maantang Formation as their hydrocarbon supply.The natural gas of Yongxing comes from the shale source rocks of the second Member of Maantang Formation.Oil and gas accumulation models and the scale of fault development are the main factors controlling the difference of gas reservoir characteristics and natural gas sources in different structures of Leikoupo Formation in western Sichuan Basin.
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万方数据
