Geological background
Fig. 1 shows the current Mechanical Mechanisms diagram of north-west Qaidam basin. Located on the binding of Ancient Asian and Tethys-Himalayan tectonic domains, Qaidam Baisin suffered great complicated tectonic stress which resulted in significant uplifted structure.
The action of NS compressional stress has been the major Mechanism and Dynamic Sources of most tectonic uplifts in the region. Meanwhile, the compression stress produced two sets of shear stress, of which one was parallel to the Altun Tagh fault. These two sets of shear stress made the tectonic uplifts in the west region take a clockwise rotation. It formed a series of "S type" anticlines there. Moreover, the Tertiary uplift which formed by the actions of NS compressional stress is the main oil-bearing structure within the region (Sun, 2004; Deng, et al., 1998; Dai, et al., 2000).
The north-west region was the major depressed area in Oligocene-Pliocene Epoch of Qaidam Basin, and it is the main current petroleum province of the basin. The Tertiary strata of Qaidam basin includes Lulehe Formation (E1+2), Lower Ganchaigou Formation (E3), Upper Ganchaigou Formation (N), Lower Youshashan Formation (N12), Upper Youshashan Formation (N22), and Shizigou Formation (N32) from bottom to top (Liu, 2003). Previous research has roughly classified the Tertiary sedimentary facies of the North-West Qaidam Basin, but some are not quite exact, especially the classification of sedimentary microfacies. Through research, the thesis systematically analyzed the sedimentary microfacies of period E1+2, E31and E32, and then established the distribution of sedimentary microfacies and the evolution of sequence depositional facies.