Abstract: According to the depositional, structural and hydrochemical features in Gunan sub-sag, the hydrogeological process is divided into 3 cycles of hydrogeology of Middle-U pper Eocene to Lower Oligocene in abnormal pressure, Middle-U pper Oligocene in transitional pressure and Miocene to Quaternary. The evolution of hydrodynamic field in this sub-sag underwent 5 stages of Es₃-Es₂ members which are the major zones of petroleum generation and accumulation. Nowadays, the hydrody namic field assumes compaction-driven flow, being of significant controls on the petroleum migration and accumulation. It is found from simulation of paleo-hydrodynamic field of petroleum migration stage of major reservoir (Shahejie formation) that it is the compaction-driven flow of this stage that al low the petroleum to accumulate tow ards the margin of Gunan sub-sag into crossflow discharge areas followed by shaping three accumulations of the Gudong fault zone in eastern the sub-sag,the upthrow side of Gunan fault in northwestern the sub-sag and the slope in southwestern the sub-sag.

Key words: Gunan oilfield, hydrogeology, hydrodynamic condition, petroleum migration, petroleum accumulation