Page 318 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Spontaneous imbibition 291

Table 10.1 Oil recovery factors (RF, %) by 138 days at different initial wettabilities.
Conventional rock Shale rock

Permeability, mD 120 3.3E-04
Porosity 0.24 0.1
RF, initially oil-wet rock (no 0.0 0.0
surfactant added)
RF, initially water-wet rock (no 42.6 38
surfactant needed)
RF, initially oil-wet changed to 45.0 0.01
intermediately wet
(IFT ¼ 0.008 mN/m)
RF, initially oil-wet changed to 46.9 13.0
water-wet (IFT ¼ 0.008 mN/m)
RF, initially oil-wet changed to 41.2 5.0
intermediately wet
(IFT ¼ 20 mN/m)
RF, initially oil-wet changed to 44.9 41.1
water-wet (IFT ¼ 20 mN/m)

the oil recovery factors from spontaneous imbibition are similar for the con-
ventional rock and the shale rock. Recall from the preceding section that
when the rock is initially oil-wet, the oil recovery factors are very different
as shown in Fig. 10.2.
To further explain our point, the oil recovery versus time is plotted in
Fig. 10.5 for the two cases: initially water-wet rock and oil-wet rock but
slowly altered to water-wet by surfactant. It shows that the oil recovery fac-
tor in the former case quickly reaches to the maximum recovery factor of
42.6%, while in the latter case, the oil recovery is very slow because it takes

Figure 10.5 Comparison of oil recovery curve of the initial water-wet case with that of
the case of initially oil-wet slowly altered to water-wet by surfactant.