Geochemical characteristics and sources of natural gas in Hangjinqi area of Ordos Basin
In order to clarify the differences of characteristics and sources of natural gas in different zones in Hangjinqi area of Ordos Basin,the geochemical composition characteristics of natural gas in three major explora-tion zones in Hangjinqi area were compared and analyzed in detail by means of gas composition analysis and carbon isotope analysis,and sources of natural gas in different zones were discussed based on the differences in the process of gas accumulation in different zones.The results show that the natural gas of the study area has a high content of hydrocarbon gases(mainly methane),and the drying coefficients are mostly lower than 0.95,suggest-ing that the natural gas is dominated by wet gases.The non-hydrocarbon gases are mainly carbon dioxide and nitrogen,which have lower contents.The carbon isotopes δ13C1,δ13 C2 and δ13 C3 of natural gas show a positive carbon series distribution,but there are differences among natural gas carbon isotopes compositions in different zones.The δ13 C1 value of natural gas in Shiguhao zone is the heaviest,and the δ13 C2 and δ13 C3 values of natural gas in Xinzhao zone are significantly heavier than that in the other two zones.The genetic analysis results show that the natural gas in the three regions of the study area is of organic genesis,showing the characteristics of coal-type gas(humus-type gas),and the main body is kerogen primary cracking gas,and the source rocks are in the stage of high-mature to over-mature thermal evolution.Combined with the results of gas-source correlation and geological background,it is inferred that the natural gas in Xinzhao zone is mainly derived from the underlying source rocks of Shanxi Formation,and the natural gas in Duguijiahan and Shiguhao zones is sourced from the source rocks of Taiyuan and Shanxi formations in the southern part of the fault,but Taiyuan source rocks contribute more.
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