Page 246 - Enhanced Oil Recovery in Shale and Tight Reservoirs

EOR mechanisms of wettability alteration and its comparison with IFT 229

50
Only kr altered
WW+IFT
45 IW+IFT
OW+IFT
40
Only Pc altered
35
Recovery factor, % 25
30

20

15
10
5
0
0 20 40 60 80 100 120 140 160
Imbibition time, day
Figure 9.7 Effect of the combined wettability alteration and IFT reduction in sponta-
neous imbibition.
Table 9.2 u in difference cases.
Case u for k r u for p c
OW þ IFT 0 0
WW þ IFT 1 1
IW þ IFT 0.5 0.5
Only pc altered 0 0.5
Only k r altered 0.5 0

As discussed earlier, wettability alteration can result in the changes in p c
and k r . To quantify the effects of p c and k r , two extra cases are compared.
One case is “Only Pc altered,” in which the oil-wet p c is changed to the
intermediately wet p c , but k r is assumed not changed. Correspondingly,
the interpolation parameter u for p c is 0.5, and u for k r is 0. Compare the
cases of “OW þ IFT” and “Only Pc altered.” When only p c is changed
from the oil-wet p c to the intermediately wet p c , the oil recovery is higher
in the early days, but the ultimate recovery is lower than that in the
oil-wet case with IFT reduction. The result indicates that the capillary imbi-
bition only improves the recovery in the early time.
The other case is “Only kr altered” in which the oil-wet k r is changed to
the intermediately wet k r , but p c is assumed not changed. Correspondingly,
u for p c is 0, and u for k r is 0.5. When only k r is partially changed from the