Page 226 - Principles of Applied Reservoir Simulation 2E

Part III: Case Study 2! 1

NB oi - (N - N p)B o = W e - W pB w

The two unknowns in the equation are N and W e.
The simplest production scenario is to assume that water influx is
negligible, that is, W e - 0. If we further observe that water production W p is in-
significant, we have
N B
N = p

where B oi = 1.3473 RB/STB at P ( = 3935 psia. Oil FVF has been corrected for
use in this calculation (see Chapter 20 for details). The corresponding estimate
for OOIP is N ~ 1500 N p with B 0 - B oi ~ 0.0009 RB/STB. The results of the
calculation are presented in Table 21-1.
Table 21-1
Results Assuming No Water Influx
Time Pressure B. N , N
(days) (psia) (RB/STB) (MSTB) (MMSTB)
91 3898 1.3482 46 69
183 3897 1.3482 91 136
274 3895 1.3482 137 205
365 3892 1.3483 183 274

The value of/^increases at each time. This implies that the material balance
model does not account for all of the pressure support and suggests that an
aquifer influx model should be considered.
If we use a volumetric estimate ofN, namely N vol = 8.5 MMSTB from
Chapter 21.1, we can calculate W e. Again recognizing that W p ~ 0, the material
balance equation becomes

W € = N(B oi - B o) + N pB 0

Results of the calculation are shown in Table 21-2.