Abstract:

Four types of fluid inclusions occur in the coal seam roof in the Liulin area including the brine liquid hydrocarbon,
liquid-gas hydrocarbon and gas hydrocarbon. They are mainly trapped either in the quartz overgrowth and fracture of sandstone
or in recrystallized calcites and solution holes filled calcites of limestone. Based on the thermodynamic of fluid inclusions, the
fluid inclusions in the Shanxi Formation were classified as types of low-temperature and low salinity and of high-temperature
and high salinity, while those in the Taiyuan Formation were defined as types of low-temperature and composite-salinity and
of high-temperature and high salinity fluids. Types of the fluid inclusions in the Taiyuan Formation testified the superimposed
impact of the paralic coal-forming environment to the connectivity with surface freshwater in the later period. It was suggested
that, according to the fluid inclusions types, micro-fluorescence and thermodynamic characters of the fluid inclusions and in
combination with the geothermal evolution analysis, the first stage of the hydrocarbon injection in the Liulin area occurred during
Middle to Late Triassic with relatively low amount of hydrocarbon generation. The second stage which was a major period of the
hydrocarbon generation occurred during Early Cretaceous with prolific gas inclusions and high hydrocarbon generation intensity.

Key words: Fluid inclusion, coal-derived hydrocarbon, paleo-geothermal history, Liulin, Ordos Basin