Page 362 - Enhanced Oil Recovery in Shale and Tight Reservoirs

334 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 11.21 Oil recovery factor and pressure during huff-n-puff for the high-IFT
solution.
when the oil during the huff and soaking periods is added together
compared to the oil added during the puff periods, as shown in Fig. 11.22
(experimental data). In this figure, the huff and soaking time varied, but
the depletion (puff) time was the same (12 h), total eight cycles. Interest-
ingly, the oil recovery during the 3 h of huff and soaking was even higher
than that during the 12 h of depletion for eight cycles. During the depletion,
the pressure was low at practically atmospheric pressure because the pressure
was immediately depleted, and the imbibition is actually spontaneous imbi-
bition. These data suggest that the pressurized imbibition is important; in
other words, the pressure helps imbibition.
For the above one brine, one low-IFT and one high-IFT surfactant
solutions, spontaneous imbibition, forced imbibition, and cyclic injection

Figure 11.22 Oil recovery factors for different huff and soaking times compared to that
during 12 h of depletion (high-IFT cases).