Characteristics of paleo-fluid and hydrocarbon accumulation significance of the Jurassic reservoir in the Kedong structural belt in the western Kunlun Mountains

Crude oil was obtained from the Jurassic reservoir in well Fusha-8 located in the Kedong structural belt Study of this reservoir has promoted the exploration for new zones and new reservoir types in the western Kunlun Mountains. Petrography, microthermometry of fluid inclusions, homogenization temperature, quantitative grain fluorescence (QGF) and quantitative grain fluorescence on extract (QGF-E) are used to study the paleo-fluid characteristics and hydrocarbon charging periods of the Jurassic reservoir in the Kedong structural belt. Results show that there were two generations of hydrocarbon inclusions in the reservoirs rocks: the first stage is hydrocarbon inclusions with yellow, yellow-green fluorescence distributed as plate-like or point, color, which indicated the filling of early oil; the second stage is hydrocarbon inclusion with blue-white fluorescence, distributed line-like along fractures, which indicated the filling of late oil. The QGF index is mainly distributed between three and seven % which showed hydrocarbon filling in early periods, and residual oil reservoirs may have existed. QGF-E indexes mainly range from 9.6 to 74, indicating characteristics of condensate oil and light oil, and their characteristics are similar to the characteristics of hydrocarbon inclusions with blue-white fluorescence. Homogenization temperatures of coeval aqueous inclusions show two peaks at 95~105 ℃ and 115~125 ℃. Combined with simulation analysis of burial history and thermal evolution history, two stage hydrocarbon accumulation was identified. The first is the filling of oil since 20 Ma, formed with relatively low maturity hydrocarbon inclusions emitting yellow fluorescence and in the second stage (since 5 Ma) mainly formed with relatively high maturity hydrocarbon inclusions emitting blue-white fluorescence. QGF and QGF-E showed that the Jurassic paleo-oil reservoirs were formed in the early period and now existing condensate or light-oil reservoirs in the Kedong structural belt.