The Material Balance Approach vs Reservoir Simulation as an Aid to Understanding Reservoir Mechanics

Recent years have witnessed great strides il reservoir simulation techniques. Numerous reservoir simulators have been developed, and are bein! employed in comprehensive reservoir production optimization studies. With increased emphasis on total simulation employing mathematical models, one cannot help wondering whether the classical material balance methods are passe’. The present article attempts to demonstrate the value of material balance type studies as aids to gaining an understanding of oil reservoir behavior. The generality of the material balance approach is discussed, that is, the employment of a single material balance equation, but,in certain prediction calculations, different saturation equations for different combinations of the basic oil production processes, i.e. gas cap expansion (with gravity segregation, with or without counterblow) solution gas drive, and water drive. LiiiiitatiOiiS of this method, as well as certain complicating features, are pointed out. Both integral and differential forms of overall material balances are discussed, and some of the basic characteristics of each, which are often overlooked, are brought out.