Abstract: Abnommal high pressure is found from Neogene to Jurassic in Lenghu-Nanbaxian structural belt in the northern margin of Qaidam basin, and mostly occurs in undercompaction shale. It was primarily formed by undercompaction, hydrocarbon generation and tectonic compression. The shale caprocks in Jurassic primary hydrocarbon reservoir and Tertiary secondary reservoirs are both abnormal high pressure zones and good pressure-sealed ones, which control the vertical distribution of hydrocarbons. The study shows that the under the abnormal high pressure zone which can be as a good sealing or cap rock is favorable for hydrocarbon enrichment and for exploration and development in northern margin of Qaidam basin.

Key words: Qaidam basin, northern margin, abnormal high pressure, origin, sealing