Abstract: The porosity evolutional function controlled by buried depth and time in Y inggehai basin is established, by which paleothickness and paleodepth of the strata are given; and paleopressure of formation is predicted by the model with modifed Pillipone formula, the error correction is then made by using observed formation pressure; finally, the paleo-fluid potential is estimated based on the paleodepth and paleopressure. The comprehensive analysis of fluid potential evolution from petroleum accumulation stage to present indicates that obv ious differences occur in control of the evolution of paleofluid potential and its distribution characteristic to the natural gas migration and accumulation in different areas and different horizons. It is concluded that the natural gas generated from Y inggehai depression area tends to accumulating towards low fluid potential zone, and DF 1-1 structural belt and Yingdong slope belt could be favorable areas for gas accumulation.

Key words: Yinggehai basin, fluid potential, formation pressure, porosity, buried depth, gas migration, gas accumulation