Page 29 - Principles of Applied Reservoir Simulation 2E

14 Principles of Applied Reservoir Simulation

Substituting Eq. (2.4) in Eq. (2.3) gives the general material balance equation
in the form

(2,5)

The terms in Eq. (2.5) have a physical significance. The terms on the right
hand side of Eq. (2.3) represent fluid production and injection, while the terms
on the left hand side represent volume changes. The significance of the terms
Is summarized in Table 2-1.

Table 2-1
Physical Significance of Material Balance Terms

Term Physical Significance

ND 0 Change in volume of initial oil and associated gas
ND Change in volume of free gas
,o
MA. + Arw) Change in volume of initial connate water
Change in formation pore volume
ND r
#A Cumulative oil production
*AA Cumulative gas produced in solution with oil
GA Cumulative solution gas produced as evolved gas

GptPgc Cumulative gas cap gas production
Gfi,' Cumulative gas injection

Cumulative water influx
WJB W
wp w Cumulative water injection
*A Cumulative water production

Equation (2.3) is considered a general material balance equation because
it can be applied to an oil reservoir with a gas cap and an aquifer. The derivation
of the material balance equation is based on several assumptions: the system is
in pressure equilibrium; the system is isothermal; available fluid property data
are representative of reservoir fluids; the reservoir has a constant volume;