Hydrocarbon Generation And Expulsion History Of Source Rocks And Natural Gas Accumulation Period In The Upper Paleozoic Of The Linxing Block, Ordos Basin

With the deepening of exploration and development of unconventional oil and gas resources,tight sandstone gas industry has become an important component of China's oil and gas resources.The Linxing block is located in the eastern edge of the Ordos Basin and has abundant tight sandstone gas resources.However,due to the low exploration level in this area,the thermal history of the system has not been developed for the tight gas in the Upper Paleozoic,and the history of hydrocarbon generation,expulsion,natural gas formation and hydrocarbon accumulation period has not been studied which has led to unclear understanding of the mechanism of tight gas accumulation and difficulties in the selection of favorable exploration zones.Three sets of source rocks from the Benxi Formation,Taiyuan Formation and Shanxi Formation in Linxing Block were evaluated in terms of geological features,organic geochemical characteristics and hydrocarbon generation capacity.The results show that source rock including carbonaceous mudstone and dark mudstone and coal in the Linxing Block,coal has the strongest hydrocarbon-generating ability,carbonaceous mudstone and dark mudstone have little difference.As a whole,the hydrocarbon generation intensity of the source rocks is generally greater than 10×10~8m~3/km~2,and it provides the gas source conditions for the formation of a giant gas field.Through literature research,data analysis,sample testing and other methods,a series of parameters needed for basin modeling were determined.Using the basin modeling method,a geological model of Linxing block was established and the history of burial,thermal,hydrocarbon generation and hydrocarbon expulsion were restored.According to geological analysis and basin simulation results,the four stages of hydrocarbon expulsion from the source rocks in the Linxing block have been determined.They are:begin from the Middle Triassic,and rapid from the Late Triassic to the Middle Jurassic.The peak from Jurassic to Early Cretaceous,slow from Late Cretaceous to present day after uplift.Based on the results of comprehensive basin modeling and fluid inclusion analysis,the natural gas accumulation stages of several major gas strata in the Tai 2,He 8and Qian 5 sections of the Upper Paleozoic of the Linxing block were identified,revealing the gas was charged continuously from Late Triassic to Early Cretaceous.The peak charge period was Late Jurassic to Early Cretaceous.The continuity was slightly weakened in the middle period,the inner-source was the earliest,followed by the near-source and the far-source.