Abstract: It is an irreversible process and a dissipated structure with space-time match for petroleum migration and accumulation. The sedimentary water is the carrier and main driving force of petroleum migration and accumulation, which controls the fluid movement and appears centrifugal flow from the center to edge of basin, while penetrated water fommed by infiltration of atmospheric precipitation and surface water appears centripetal flow from the edge to center of basin by gravity process. The result is that press equilibrium zone is formed under the processes, where oil and gas can be accumulated. A big oilfeld could be formed by a lrap with the upper equilibrium structure preserving petroleum and the lower dissipated structure injected with oil and gas continuously. The hydrodynamism is also of significant effect on petroleum preservation and destruction.

Key words: oil-gas field, hydrocarbon accumulation, hydrodynamics, dissipated structure, Biyang sag