Thermal histories of 24 wells in Qikou sag are simulated by using vitrinite reflectance data.The simulation results show that the geothermal gradients are about 5.0～ 5.6℃/100 m during the deposition of Shahejie Fm

4.5～5.0℃/100 m during the deposition of Dongying Fm

and 3.5～4.5℃/100 m during the deposition of Guantao Fm

respectively.The current geothermal gradient is measured to be about 3.1～3.2℃/100 m.Based on the homogenization temperatures of fluid inclusions

the restored burial history of core samples

and the thermal evolution and hydrocarbon generation histories of source rocks

there are two hydrocarbon charging stages in the study area.The first charging stage occurs at the end of deposition of Dongying Fm;the second charging stage extends from the end of deposition of Guantao Fm to present time

and is the main charging stage of hydrocarbons in Qikou sag.Hydrocarbon migration and accumulation modeling with PRA 2D simulation software also show that there are two hydrocarbon accumulation peaks in Qikou sag

with the first one at the end of deposition of Dongying Fm and the second one from the end of deposition of Guantao Fm to present time.