Page 413 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Fracturing fluid flow back 383

Figure 12.40 Oil recovery by spontaneous imbibition during the soaking process in
(A) tight cores and (B) conventional cores.

Figure 12.41 Experimental apparatus for invasion and flow back.
which had a low IFT and a water-wetting angle had the lowest permeability
ratio and flow back efficiency. In those experiments, the capillary numbers
7 6
were in the order of magnitudes of 10 e10 (Tangirala and Sheng,
2019b). Such low capillary numbers may not make the capillary desaturation
mechanism work (Sheng, 2011). Thus, the mechanism that might play in
those experiments was wettability. Since the cores were initially oil-wet,
the invaded zone closer to the end B was oil-wet in the water case. Then
the oil from the end A could imbibe into the invaded zone of the core close
to the end of B. The capillary pressure was the driving force which helped