Page 140 - Fundamentals of Enhanced Oil and Gas Recovery

128 Pouria Behnoudfar et al.

volume is reduced by the volume of invading water. Therefore, the mass of required
, is obtained by [58]
CO 2 in a reservoir, M CO 2
5 ρ (4.35)
ð
M CO 2 RF A h [ 1 2 S wi Þ 2 V iw 1 V pw
CO 2
where RF, A, h, ρ , V iw , V pw , and S wi are recovery factor, area, net pay thickness,
CO 2
CO 2 density at reservoir conditions, reservoir volume of invading water, reservoir vol-
ume of produced water, and initial water saturation, respectively. Most of this infor-
mation can, generally, be found. The volume of injected or produced water can be
calculated from production records.
The same methodology applies in the case of solvent- or gas-flooded reservoirs. If
CO 2 EOR is done in a reservoir after a hydrocarbon flood, then immiscible gas is dis-
placed along with oil by CO 2 and the vacant volume will be available for CO 2
sequestration [118].
In waterflooding, a common practice to obtain the ultimate recovery is to plot
fractional recovery with respect to WOR on semilog paper and extrapolate the results.
The same logic can be utilized to determine the recovery in gas floods [116].
The overall reservoir recovery for a fully developed waterflood reservoir can be
estimated as follows:

E 5 mX 1 n (4.36)
where

1 1

X 5 ln 2 1 2 ; (4.37)
f w f w
1
m 5 ð 1 2 S wi Þ (4.38)
b

1 1
n 52 S wi 1 lnA (4.39)
1 2 S wi b
μ

A 5 a w (4.40)
μ o

and a and b are obtained from k o =k w 5 e bS w .
According to this procedure, recovery of gas flooding can be estimated by substi-
tuting gas parameters instead of water ones into the relations. Hence, the final equa-
tions can be simplified as
5:615 1
5 2 1 (4.41)
R f g