Abstract:  The distribution of industrial gas wells in the northern and southern regions of the Boerjianghaizi fault in Hangjinqi area of Ordos basin does not match the evolution degree of the source rocks, and the natural gas accumulation periods between the northern and southern regions of the fault are different. On the basis of the evolution history of source rocks and fault development history, combined with the carbon isotopes of natural gas components, the dry coefficient of natural gas, the characteristics of fluid inclusions and the sealing property of the fault in different directions, this paper compares the source, accumulation period, accumulation time and migration channel of natural gas in the northern and southern regions of the fault. The results show that the carbon isotopes of the natural gas components present “positive carbon isotope sequence”, namely, δ13C1<δ13C2<δ13C3, suggesting that the natural gas in the study area comes from a single source. The dry coefficient of natural gas in the southern part of the fault ranges from 0.85 to 0.96, with an average value of 0.91. In the northern part of the fault, the dry coefficient of natural gas ranges from  0.95 to 0.97. The homogenization temperature of aqueous inclusions coexisting with natural gas inclusions in the Xiashihezi  Formation reservoir ranges in 95115 ℃ and 125135 ℃ in the southern area of the fault, and in 75155 ℃ in the northern part of the fault. Combining with the burial history of the study area, there exist two stages of gas accumulation in the southern part of the fault, the earlystage natural gas charged from Late Jurassic to the Early Cretaceous (155142 Ma), and the latestage natural gas charged at the end of Early Cretaceous (116110 Ma). There is only one stage of the natural gas accumulation in the northern region, and it occurred at the end of Early Cretaceous (128117 Ma). The Boerjianghaizi fault has been active for many periods since the Paleozoic, and the activities in the Yanshan period are the main reason for the difference of natural gas distribution, thermal evolution degree and accumulation time between the northern and southern regions of the fault.

Key words:  natural gas accumulation, fluid inclusion, Ordos basin, Boerjianghaizi fault, Hangjinqi area