## Abstract

Material balance is one of the key techniques for evaluating hydrocarbon reserves when production and pressure data from the field become available. It makes use of the basic concept of conservation of mass; which states that the cumulative observed production, expressed as an underground withdrawal, must be equal to the expansion of the fluids in the reservoir resulting from a finite pressure drop or expressed as the mass of fluids originally in place equal to mass of fluid remaining plus the mass of fluid produced. Material balance equation (MBE) is seen by the Reservoir Engineers as the basic tool for interpreting and predicting the performance of reservoirs. It helps them to get a feel of the reservoirs but has some limitations. There are several assumptions adopted in the derivation of the material balance equation and the implications which are presented herein. Therefore, to understand the material balance concept properly, several derivatives for oil and gas reservoirs to represent the general material balance equation under different conditions with multiple solved examples are presented in this chapter. Also the method of estimating the present gas-oil and oil-water contact are presented.

## Keyword

Material balance Undersaturated reservoir Saturated reservoir Production data PVT data Aquifer influx Drive mechanisms Gas reservoir STOIIP FGIIP Depletion drive Water drive Segregation drive Production characteristics## Supplementary material

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