Abstract: Based on the special geologic and hydrodynamic features, the conventional material balance equation is modified.The hydrocarbon and bottom water underlying oil zone are considered as oil reservoir system; water zone out of oil area as water system, by which the material balance equation for thin-layered bottom water reservoir is established.Then common edged-water influx model is used to calculate aquifer size of this type bottom-water reservoir.Also, in order to validate the reliability of this method, 3D reservoir numerical model for bottom water or aquifer is developed and the correlation study of numerical simulation is conducted.The result shows that the bottom water or aquifer size predicted by the two methods is similar to each other, indicating that the method given by this paper is simple, reliable and practicable for use.

Key words: bottom-water reservoir, material balance equation, water encroachment, numerical simulation