Features Of Jurassic Reservoir And Fluid Inclusions Analysis Of Qiangtang Basin

Qiangtang Basin is the composite basin with the main structure of Mesozoic marine deposits developed on the base of pre-Devonian crystal. This paper discusses the features of Jurassic reservoir and fluid inclusions based on adequate collecting and arrangement of the former research productions. The Jurassic reservoir in Qiangtang Basin is widely distributing with the main lithology of clastic reservoir and carbonate reservoir rocks, in which Qoimaco formation (J2q) and Xiali formation (J2x) composite mainly by clastic reservoir, Buqu formation(J2b) and Suowa formation(J3s) composite mainly by carbonate reservoirs, and Xueshan formation(J3x) composites with both. The reservoir fluid inclusions is comparatively with less quantity and smaller size. The smallest one is below 3mm, and the biggest one is no more than 30mm, with normal size between 5 and 10mm. The shape of the fluid inclusions is similar square, or rotundity or ellipse, and so on with comparatively regular, as well as other irregular inclusion. The inclusions are naturally random distributing with situation, as isolated, starred, scattered and so on. The Phase behaviors under the indoor temperature(25℃) are main including liquid H₂O inclusion, gas-liquid H₂O inclusion, liquid state hydrocarbon inclusion, gas-liquid hydrocarbon inclusion, asphaltum inclusion and gas state hydrocarbon inclusion. After testing, the gas-liquid inclusion homogenization temperature varies between 103℃and 195℃(mostly varies between 130℃and 180℃),with average of 147℃; The salinity variation range varies between 0.35% and 2.07%,with average of 1.08%. Laser Raman Spectroscopic Analyses shows that the component of either the liquid state inclusion or the gas-liquid inclusion mainly is water. According to the homogenization temperature, we can find out that the oil and gas in this area are in maturation-high maturation evolution stage. From the calculation result of inclusion homogenization temperature and paleogeothermal gradients, the depth of oil reservoir varies between 2075m and 4375m,with mainly between 3100m and 4025m. From the shadow on the curve graph of geothemal bury history in Qiangtang basin, the oil-gas generated between 100Ma and 150Ma, in the late Jurassic to early cretaceous.