| Tahe Oilfield locates in the margin of Akekule uplift in north Tarim Basin. It underwent several times of tectonic uplifts during middle Caledonian to early Hercynian epochs, which led to Ordovician carbonate formations being exposed perennially to the surface and suffering from intense meteoric fresh-water weathering, leaching and dissolving. At the same time, it also went through wide marine transgression from north to south during Mid-Caledonian movement, wide marine transgression from west to east during Carboniferous period, and volcanic events during Permian period in Tahe aera. Geochemical analysis of trace elements including B, V, Ga, Rb, etc. and analysis of fluid inclusions are taken for 33 basic samples of rgillite-fillings in karst caverns from 11 wells in the main area of Tahe Oilfield. It is proved that the meteoric water karstification is predominant in this area, succeeding by reconstructing the mixed marine/meteoric water karstification and hydrothermal water karstification. There are three karstification zones in vertical in this area. The isotopic element dating of K-Ar in illite samples from the cavern fillings reveals the karstification chronogenesis that is later in the upper and earlier in the lower. The first and second karstification zones in shallow were reconstructed by marine water transgression and the third karstification zone in deep was by hydrothermal water transgression. |
