Abstract: Different features of petroleum distribution, migration and accumulation in different structural belts and sag areas occur in the west part of northern margin of Qaidam basin, due to the differences in geologic condition and environment. The main geologic factors for these differences include the fault and unconformity that control the lateral and vertical migration of oil and gas, the source rock-reservoircap rock assemblage that controls the oil-gas distribution horizons and the burial depth that determines the phase of oil or gas. In addition, the fault could result in the formation of most traps, thus affecting the preservation of oil-gas reservoirs. It is these that are determine the petroleum distribution characteristics in the west part of northern margin of Qaidam basin, namely, being belts from north to south, with oil in the south and gas in the east in lateral direction; in the vertical the petroleum is mainly accumulated in anticline traps of footwall of shallow slip fault and upper wall of deep basement fault. These geologic factors still control the types of petroleum reservoirs and the oil-gas migration and accumulation patterns in different areas and tectonic units.

Key words: Qaidam basin, reservoir distribution, petroleum migration, petroleum accumulation, difference, fault