Research On Fluid Inclusions Of The Reservoirs In The Upper Paleozoic In The Northeast Of Ordos Basin

In this paper, we researched 120 slices of fluid inclusions in Taiyuan, Shanxi, Shihezi and Shiqianfeng formations of Upper Paleozoic in Yulin-Zizhou area, through testing homogeneous temperature and freezing point of fluid inclusions in different diagenetic stages and calculating salinity, density and fluid potential to determine the accumulation periods of gas pool and finally point out the gas main gathering area.By observation on inclusion petrography, the host minerals of fluid inclusions are mainly quartz, and fluid inclusions output in quartz particles, the secondary side and healed cracks in quartz. They are mainly small in shape, mostly round and oval-based. Because of different types, they are different in color, some are transparent, brown, gray-black and dark brown and so on. Vertically from Taiyuan to Xiashihezi, the abundance of hydrocarbon inclusions decreases, the individual gradually becomes smaller; from south to north, the gas-liquid ratio of containing gaseous hydrocarbon inclusions decreases. Because of differences in phase composition, we divided the fluid inclusions in the study area into five types. The majority type is containing gaseous hydrocarbon inclusions, which implies that a higher degree of gas evolution in this area.By analyzing the composition features of inclusions and comparing methane carbon isotope trend of gaseous hydrocarbon inclusions and gas reservoir in different layers, the methane carbon isotope of gaseous hydrocarbon inclusions in Taiyuan, Shanxi group and He8 is relatively light, while the methane carbon isotope of present reservoir is heavier overall. The CH4 component in He8, Shanxi and Taiyuan increases from north to south, suggesting that the higher degree of thermal evolution of the south. Comprehensive analysis that the present gas reservoir is a cumulative result of gas accumulation, and still maintain the dynamic fractionation process.The hydrocarbon charging period are decided by inclusion homogeneous temperature and terrestrial heat history. It can be divided into two times in the Taiyuan formation, of which the first accumulation time of the Early Jurassic period and the second accumulation time of the late of the Middle Jurassic to the late of the Early Cretaceous period play great significant roles in the gas accumulation here.There are two gas accumulation times in the Shanxi formation.The first accumulation time is the early of Early Jurassic to the early of the Middle Jurassic period. The second accumulation time of the late of the Middle Jurassic to the late of the Early Cretaceous period and the last one play great significant roles in the gas accumulation here.It can be divided into two times in the Shihezi formation, of which the first accumulation time of the late of the Early Jurassic to the the late of the Middle Jurassic period and the second accumulation time of the Late Jurassic to the late of the Early Cretaceous period play great significant roles in the gas accumulation here.The gas accumulation time of the Shihezi formation is the Late Jurassic to the late of the Early Cretaceous period.Natural gas carbon isotope analysis showed that the Upper Paleozoic of Ordos Basin, gas lines with different content of methane carbon isotope heavier, has the characteristics of coal gas. Ethane, propane carbon isotope are typical characteristics of coal into a gas. Comprehensive analysis that at a gas reservoir is the result of a cumulative gas gathering, gas reservoir present within the distillation process remains dynamic.Through restorating fluid potential obtained that fluid migration in the basin mainly northeast-southwest oriented, essentially from the southwest to the center of the basin and northeast. The southwest of basin has the relatively high potential at the end of the Yanshan period, but the surrounding has the low fluid potential, especially in the northeast of the basin has low fluid potential gradient as the main migration area.