| Summary: | This paper summarizes the genetic causes of hydrodynamic pressure distribution based on study of theoretical mechanisms and reservoir cases and determines the causes of the 4th Pay in the Zubair Formation of the Rumaila Oilfield using exclusive method and numerical simulation. These causes can be classified into three types as the hydrodynamic aquifer type, the reservoir compartmentalization type and the changing fluid density type. Among them, the hydrodynamic aquifer type may result from depletion of hydrodynamic pools or adjacent oilfields. The aquifer pressure in the 4th Pay reservoir decreases from north to south, without tilted oil-water contact. Considering the geological settings of the 4th Pay reservoir, its hydrodynamic pressure distribution is hydrodynamic aquifer. By numerical simulation of the pressure distribution, fluids contacts geometry and adjusting time, the hydrodynamic aquifer in the 4th Pay is due to the depletion of adjacent oilfields. Combining regional geological setting and investigation of production history of adjacent oilfields, the hydrodynamic pressure distribution phenomenon in the 4th Pay reservoir is affected by the depletion of the Raudhatain oilfield in the south. Key words: aquifer pressure, hydrodynamics, tilted fluid contact, hydrodynamic aquifer, changing fluid density, depletion drive
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