Page 28 - Principles of Applied Reservoir Simulation 2E

Part I: Reservoir Engineering Primer 1 3

provide an independent method of estimating the volume of oil, water and gas
in a reservoir for comparison with volumetric estimates. The magnitude of
various factors in the material balance equation indicates the relative contribution
of different drive mechanisms at work in the reservoir. Material balance can be
used to predict future reservoir performance and aid in estimating cumulative
recovery efficiency. More discussion of these topics can be found in references
such as Dake [1978] and Craft, et al. [1991],
The form of the material balance equation depends on whether the
reservoir is predominately an oil reservoir or a gas reservoir. Each of these cases
is considered separately.

Oil Reservoir Material Balance
The general material balance equation for an oil reservoir is the Schilthuis
equation [1961] expressed in a form given by Guerrero [1966]:

(2.3)

-TV R B -{W+W.-W)B
p so g \ e i p J w

All of these terms are defined in the Nomenclature at the end of this chapter. The
unit of each quantity is presented in square brackets in the Nomenclature. The
physical significance of the terms in Eq. (2.3) can be displayed by first defining
the terms
B -B .

_
D "
(2.4)
l-S wlg B twi
B ticAP.
« /