Hydrodynamic Evolution and Hydrocarbon Accumulation in the Dabashan Foreland Thrust Belt,China

There are two plays in the Dabashan foreland tectonic belt:the upper and the lower plays. The lower play experienced one sedimentary hydrodynamic stage,two burial hydrodynamic stages, two tectonic hydrodynamic stages and two infiltration hydrodynamic stages from the Sinian to the Cenozoic,while the upper play had one sedimentary hydrodynamic stage,one burial hydrodynamic stage,two tectonic hydrodynamic stages and one infiltration hydrodynamic stage from the Permian to the Cenozoic.Extensive flows of both sedimentary water,including hydrocarbons,and deep mantle fluid occurred in the Chengkou faults during collision orogeny in the Middle-Late Triassic Indosinian orogeny,and fluid flow was complicated during intracontinental orogeny in the Middle-Late Jurassic. In addition to these movements,infiltration and movement of meteoric water took place in the Chengkou faults,whereas in the covering-strata decollement tectonic belt,extensive sedimentary water flow(including hydrocarbons) occurred mainly in the Zhenba and Pingba faults.During the stage of rapid uplift and exhumation from the Cretaceous to the Cenozoic,the fluid flow was characterized mainly by infiltration of meteoric water and gravity-induced flow caused by altitude difference, whereas sedimentary water flow caused by tectonic processes was relatively less significant. Sedimentary water flow was more significant to the lower play in hydrocarbon migration and accumulation during collision orogeny in the Middle-Late Triassic Indosinian orogeny,but its influence is relatively slight on the upper play.On one hand,hydrodynamics during intracontinental orogeny in the Middle-Late Jurassic adjusted,reformed or oven destroyed oil reservoirs in the lower play;on the other hand,it drove large amounts of hydrocarbons to migrate laterally and vertically and is favorable for hydrocarbon accumulation.Infiltration hydrodynamics mainly adjusted and destroyed oil reservoirs from the Cretaceous to the Cenozoic.