Page 301 - Enhanced Oil Recovery in Shale and Tight Reservoirs

274 Enhanced Oil Recovery in Shale and Tight Reservoirs

q ffiffiffi
ffiffiffiffiffiffiffiffi . The ratio of water volume (V wsi ) to oil vol-
be proportional to t k s wo cosq osi
p
4 m o m w L 2
c
ume (V osi ) by spontaneous imbibition is
V wsi cosq wsi
¼ (9.57)
V osi cosq osi
q wsi and q osi are the water-wetting angle and oil-wetting angle during
spontaneous imbibition, respectively. If V wsi > V osi , cosq wsi > cosq osi .
Then q wsi < q osi , the core is more water-wet, and vice versa. Therefore,
we have Conclusion 4:
The rock wettability can be determined by comparing the water and oil
spontaneous volumes, if the core is initially saturated with oil or water; with
higher water imbibition volume, the rock is water-wet.
During the forced imbibition, the water volume imbibed into the
initially oil-saturated core is

p 2 DF w þ 2s wo cosq ws r 6
2
V w;FI ¼ r t w;FI (9.58)
4m w
The oil volume imbibed into the initially water-saturated core is

p 2 DF o þ 2s wo cosq os r 6
V 2 ¼ r t o;FI (9.59)
o;FI
4m o
The fraction of water volume by spontaneous imbibition in the total
water imbibition volume, d w,SI ,is

r ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2s wo cosq ws
t w;SI
V w;SI r
d w;SI ¼ ¼ s ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
r ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
V w;SI þ V w;FI
2s wo cosq ws 2s wo cosq ws
t w;SI þ DF w þ t w;FI
r r
1
¼ s ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi:

DF w t w;FI
1 þ 1 þ
p cw t w;SI
(9.60)
The fraction of oil volume by spontaneous imbibition in the total oil
imbibition volume, d o,SI ,is