Keywords: 
• hydrodynamic /
• evolution oil-gas /
• migration and accumulation /
• Taibei depression

Abstract: The regional groundwater flow in Taibei depression of Tu-Ha basin is the gravit y-induced cross-formational groundwater flow. There are two gravity-induced cross-formational groundwater flow systems in Taibei depression. One is in Sheng bei sag and the other is in Qiudong and Xiaocaohu sags. The groundwater in the groundwater systems flows from north to south. The recharge area of the groundwater is in the Bogeda mountainous terrain north Taibei depression and the drainage is in the north border of the central faulted zone in Taibei depression. There is ve rti cally good hydraulic connection among the different formation waters. Since the Jurassic period，there have been three different stages of the groundwater hydro dynamic evolution. The early stage (Jurassic period) is the stage of the compacted groundwater flow，in which the compacted flow caused the large-scale oil -gas reservoir to distribute within effective source rocks around the sags of the generating hydrocarbon. In the middle stage(Cretaceous Period-Miocene Epoch)，the groundwater flow is the compacted and gravity-induced flow and it had adjusted the reservoir formed in the early stage of hydrodynamic evolution. The groundwat er caused oil and gas to accumulate in the mixed zone of the compacted and gravi ty-induced groundwater flows. In the late stage(Pliocene Epoch to now)，the grou nd water flow is driven by topography and it had the interface of oil/water，the oil saturation of reservoir and the oil-gas-bearing formation and location chang edsignificantly along regional groundwater flow.