Page 386 - Enhanced Oil Recovery in Shale and Tight Reservoirs

358 Enhanced Oil Recovery in Shale and Tight Reservoirs

1
MeOH evaporated
0.8 MeOH removed
MeOH expelled
PV Liquid Removed 0.6

0.4

0.2

0
0.1 1 10 100 1000 10000
N PVg
Figure 12.15 Liquid (methanol) removed from Berea sandstone core by displacement
and evaporation (p mean ¼ 1.1 atm., k ¼ 327 mD, and the core length 7.6 cm) (Mahadevan
and Sharma, 2005).

the liquid (brine) removed from a Texas Cream limestone core by displace-
ment and evaporation. Evaporation started to remove brine when the flood
gas volume reached 1000 pore volumes (N PVg ). Fig. 12.15 shows the meth-
anol removed from a Berea sandstone core by displacement and evaporation.
Evaporation started to remove brine when the flood gas volume reached
60 N PVg . In this case, the rock permeability was high, and the volatile meth-
anol was used. These conditions are favorable to evaporation (Mahadevan
and Sharma, 2005). It can be predicted that in shale and tight reservoirs, it
will take much longer time for the evaporation to start to show up.

12.3.6 Permeability jail
Many field cases show that the connate water saturation is immobile at very
high saturations in low permeability reservoirs; within a large range of
middle saturation, neither gas nor water could flow (Shanley et al., 2004).
They term this range of saturation “permeability jail”. Ojha et al. (2017)
estimated relative permeabilities for shale cores using nitrogen adsorption-
desorption data. Their data show that water cannot move for water saturation
higher than 50%. Based on these facts, we may hypothesize that during the
fracturing operation, high pressure and saturation of fracturing fluid force
the fracturing fluid (water) to move deep into a formation, with help of water