Page 352 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Forced imbibition 325

Figure 11.16 Alkaline concentration map in the middle layer at 90 days in the high-p c
shale model.

spontaneous imbibition. Such result may not be applicable to the forced
imbibition (flooding) in a field scale. Therefore, we further investigate the
effect of capillary pressure in small models for 9 days of injection.
Let us further check the sensitivity of capillary pressure when the initial
wettability is oil-wet. The detailed parameters and results are presented in
Table 11.6. In these models, the function to change relative permeabilities
is removed. As the capillary pressures (both initial and altered) are increased
by the same factors of 10 and 100, the oil recovery factor decreases from
0.067 to 0.025 and 0.001, respectively. The oil recovery is sensitive to the
value of capillary pressure. For the shale model, because of the high resis-
tance from the initially oil-wet cores, the alkaline solution cannot enter
the matrix and the resulting oil recovery factors are null, regardless of the
values of capillary pressure.

Table 11.6 Effect of capillary pressure in initially oil-wet cores for 9 days.
Capillary pressure endpoint, psia (Darcy) 1/2 Recovery factor
Initially Altered Sand Shale
0.1452 0.1033 0.067 0.0
L1.452 1.033 0.025 0.0
14.52 10.33 0.001 0.0
L1.452 0.1033 0.0246 0.0
L1.452 10.33 0.0246 0.0