Abstract: The overpressure system plays a crucial role in the process of oil and gas migration and accumulation in Dongying Sag.Due to the lack of dynamic characterization of the overpressure system,this study investigates the pressure gradient characteristics and its control on oil and gas in a sequence of "point-line-surface".The research indicates that the areas with high and low gradient values overlap longitudinally.Planarly,the high gradient value in the lower part of the Fourth Member of Shahejie Formation is distributed in the northern deep sag and gradually diminishes from north to south.The high gradient value ranging from the upper part of the Fourth Member to the lower part of the Third Member of Shahejie Formation is distributed around each hydrocarbon generation sag.There exist five types of pressure gradient structures.The high pressure-low gradient zone is located at the center of the sag,followed outward by the high pressure-high gradient zone,the transition-high gradient zone,the transition-low gradient zone,and the normal pressure-low gradient zone.Source,reservoir and seal formations constitute the material basis,boundaries and structural types of the pressure gradient,with tectonic evolution controlling the vertical attenuation and spatial distribution of the pressure gradient.The oil and gas controlled by faults related to the pressure gradient are distributed in a ring-like pattern,and the related lithologic reservoirs are scattered.This study holds significant theoretical significance for rolling exploration and desert prediction in Dongying Sag.

Key words: Dongying Sag, overpressure, pressure gradient structure, controlling mechanism, oil and gas distribution