Page 272 - Introduction to Petroleum Engineering

OIL RESERVOIR MATERIAL BALANCE 259
TABLE 13.2 Nomenclature for the general Material Balance Equation

B g Gas formation volume factor (FVF) (RB/SCF)
B gc Gas cap FVF (RB/SCF)
B ′ Injected gas FVF (RB/SCF)
g
B o Oil FVF (RB/STB)
B t B + (R − R )B = composite oil FVF (RB/STB)
so
g
o
si
B ti Initial value of B (RB/STB)
t
B tw B + (R − R )B = composite water FVF (RB/STB)
sw
g
w
swi
B w Water FVF (RB/STB)
c f Formation (rock) compressibility (1/psia)
G Initial gas in place (SCF)
G i Cumulative gas injected (SCF)
G pc Cumulative gas cap gas produced (SCF)
G ps Cumulative solution gas produced as evolved gas (SCF)
m Ratio of gas reservoir volume to oil reservoir volume
N Initial oil in place (STB)
N p Cumulative oil produced (STB)
R so Solution gas–oil ratio (SCF/STB)
R si Initial solution gas–oil ratio (SCF/STB)
R sw Solution gas–water ratio (SCF/STB)
R swi Initial solution gas–water ratio (SCF/STB)
S g Gas saturation (fraction)
S o Oil saturation (fraction)
S w Water saturation (fraction)
S wi Initial water saturation (fraction)
S wig Initial water saturation in gas cap (fraction)
S wio Initial water saturation in oil zone (fraction)
W e Cumulative water influx (STB)
W i Cumulative water injected (STB)
W p Cumulative water produced (STB)
Δp p − p = reservoir pressure change (psia)
i
p i Initial reservoir pressure (psia)
p Reservoir pressure corresponding to a cumulative fluid value (psia)

The physical significance of the terms in the general material balance equation is
displayed by first defining the terms
D o B t B ,
ti
B B
D mB gc gi ,
ti
go
B gi
BS B B
D ti wio tw t twi , (13.15)
w
1 S wio B twi
mB S B B
D gw ti wig tw twi ,
1 S wig B twi
1 m
D Bc p
r 1 S 1 S tif
S
wio wig