Page 87 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

CHAPTER 4 Hybrid Chemical EOR Using Low-Salinity and Smart Waterflood 79

LSWF process. However, the pH condition less than 7.5 polymer retention. Because some polymer molecules
is observed in the secondary LSWF and it is lower than have the polyelectrolyte characteristic, the presence of
that in the tertiary LSWF. Despite the unexpected history polymer could cause exchange cations influencing the
of effluent pH corresponding to the mechanism, it is clay swelling and compatibility regime between forma-
obviously important to determine the deployment of tion and injecting brines. During the single-phase core-
LSWF as secondary or tertiary mode for successful oil flooding, the surface area of porous media is fully
production. Following the secondary LSWF, tertiary subject to the only polymer adsorption, not oil adsorp-
LSPF is successively applied. It enhances oil recovery tion, and the adsorption in the single-phase system can
by 22%, which is originated from the improving sweep be overestimated compared with that in the multiphase
efficiency (Fig. 4.11). Another experiment evaluates the system. Firstly, the effluent concentration of polymer
oil recovery from the secondary LSPF and tertiary LSWF. through single-phase coreflooding is measured to inves-
This experiment observes only 68% of OOIP after tigate the polymer retention. Two polymeric solutions
secondary LSPF and negligible improvement during of conventional polymer flood and LSPF are investi-
tertiary LSWF. In comparison between the two experi- gated for the measurements. The two cycles of core-
ments, the secondary LSPF only shows 2% higher recov- flooding are carried out for each measurement. The
ery than secondary LSWF. The tertiary LSPF produces first cycle of polymeric solution injection fully contrib-
the additional oil recovery by 18% than secondary utes to the polymer retention on the core. Therefore, the
LSPF. It is explained that the secondary LSWF is more second cycle of polymeric solution injection into the
efficient to modify wettability and redistribute the resid- same core is assumed not to be affected by the reten-
ual oil within the pore space and tertiary LSPF easily tion. To quantify the delay of polymer transport due
mobilizes the redistributed residual oil as shown in to the retention, the additional coreflooding tests inject-
Fig. 4.12. ing tracer are carried out and compared with the core-
Unsal, ten Berge, and Wever (2018) also investigated floodings of polymeric solution injection (Fig. 4.13).
the potential aspects of LSPF through single-phase The difference between the effluent profiles of tracer
displacement experiment being similar to the AlSofi, and polymer corresponds to the delay of polymer pro-
Wang, and Kaidar (2018). Unsal et al. (2018) focused duction. The coreflooding of conventional polymer
on the LSPF in sandstone reservoirs, not carbonate res- flood shows the delay of 0.35 PV (Fig. 4.13A), and the
ervoirs. The study investigated the cation exchange in coreflooding of LSPF shows the delay of 0.05 PV
the presence of polymer as well as injectivity and (Fig. 4.13B). These results correspond to the late

100 10
LS LSP

80 9
Oil recovery (% OOIP) 60 8 7 pH

40

20 LS 6
LSP
pH
0 5
0 8 16 24
PV injected
FIG. 4.11 History of oil recovery and pH through secondary low-salinity water flood and tertiary low-salinity
polymer flood. (Credit: From Torrijos, P., Iván, D., Puntervold, T., Skule Strand, Austad, T., Bleivik, T. H., et al.
(2018). An experimental study of the low salinity smart water e polymer hybrid EOR effect in sandstone
material. Journal of Petroleum Science and Engineering, 164, 219e229. https://doi.org/10.1016/j.petrol.2018.
01.031.)