Page 238 - Enhanced Oil Recovery in Shale and Tight Reservoirs

EOR mechanisms of wettability alteration and its comparison with IFT 221

saturation with the subscript wr and or for residual water and oil saturation,
respectively, q is the water contact angle with the superscript ww and ow for
water-wet and oil-wet, respectively, E pc is the capillary exponent. The effect
of IFT is treated according to Eqs. (9.2)e(9.6).

9.4.2 Adibhatla et al. (2005) model
Adibhatla et al. (2005) proposed another model explicitly including the effect
of wetting angle on residual saturations and the trapping number. The trapping
number is the capillary number including gravity effect which is discussed in
detail by Sheng (2015a). According to the existing definition of trapping num-
ber, it does not generally include the wettability effect, although it can theoret-
ically with cosq term combined with the interfacial tension s. However, such
model has not been proposed or described in detail in the literature.
Adibhatla et al.’s (2005) model requires these data: residual saturations at

two wetting angles and at low trapping number S low ; relative permeability
rj
curves at trapping number N T0 . The two wetting angles are q 0 and p q 0
corresponding to two base phases b1 and b2. In principle, these two angles
can be arbitrary. Practically, if one is strongly wetting (wetting angle close
to 0), the other one is strongly nonwetting (wetting angle close to p). We

use their notation. More generally, q 0 can be replaced by q b1 , and p-q 0
can be replaced by q b2 . A simple interpolation technique is used to consider
the wettability effect on a residual saturation at low trapping number:
S low S low S low S low
rj r;b1 r;b2 r;b1
¼ (9.12)
cosq cosq 0 cosðp q 0 Þ cosq 0
Note that oil and aqueous phases are not distinguished (a dummy phase j is
high
used). To find S rj at any trapping number, we also need S rj at two wetting
angles. Alternatively, Adibhatla et al. (2005) defined the trapping parameter
T j as a function of wetting angle:

ln T j lnT b1 ln T b2 lnT b1
¼ (9.13)
cosq cosq 0 cosðp q o Þ cosq 0
Using this new defined T j , the residual saturation at any wetting angle
and any trapping number N T is estimated from this equation:

S low S high
high rj rj
S rj ¼ S þ (9.14)
rj
1 þ T j N Tj