Page 399 - Enhanced Oil Recovery in Shale and Tight Reservoirs

370 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 12.28 Effect of shut-in on the flow back of injected fluid (leaked-off fluid).

The above base model data are used to evaluate the 10-year NPV which
is calculated by

10
X V o;i OilPrice V w;i WaterHandlingCost
NPV ¼ (12.6)
i
ð1 þ DiscountRateÞ
i¼1
where NPV is the net present value in dollars ($), V o,i is the annual oil
production volume in ith year (STB), and V w,i is the annual water recovered
volume in ith year (STB). Dollars 70/STB is taken as the oil price; the
discount rate is 10%, and the water handling cost is $7/STB water according
to Yaich et al. (2015). The other costs are assumed not affected by shut-in
time. Fig. 12.29 shows the 10-year NPVs at different shut-in times. The
NPV of each scenario is normalized by the NPV of the s0 case (immediate
flow back). It shows that the NPV is the highest (normalized NPV ¼ 1) for
the immediate flow back. As the shut-in time is longer, the NPV is lower.
Fig. 12.30 presents the effects of matrix permeability and injection value
on NPV. The range of injection volumes in barrels is 92,870 (min),106,950
(average), and 122,950 (max).When the permeability is reduced to 20 nD,