Page 88 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

80 Hybrid Enhanced Oil Recovery using Smart Waterflooding

conventional polymer flood is observed. The higher
injectivity in LSPF is explained that some polyelectro-
lyte polymer can form complexes with the divalent
ions, and the consumption of divalent ions, in turn,
forces to release the additional divalent ions from the
rock surface to bulk of polymeric solution for reequili-
brium. The formation of complexes enables to explain
the less apparent viscosity (Fig. 4.10) and differential
pressure. This study described a number of conclusions
regarding LSPF: (1) LSPF reduces the delay of polymer
propagation owing to less retention and expects the
less delay of oil bank arrival; (2) although current exper-
iments show the improved injectivity, general conclu-
sion can be developed with the more extensive
experimental observations; (3) formation of complexes
by the cation exchange between the hydrolyzed parts of
polymer and divalent cations can be another risk to
decrease the apparent viscosity of LSPF.

Experiments: Gel treatment
The polymer gels are frequently applied for the confor-
mance control to plug the high conductivity of channels
of reservoirs. The plugged polymer in fractures reduces
the fracture conductivity and mitigates the early break-
through. The high injection pressure exceeding the pres-
FIG. 4.12 Description of distribution and mobilization of
residual oil saturation after (A) secondary injection of sure of gel rupture might cause to reopen the fractures.
formation water; (B) secondary low-salinity waterflood; and The successful gel treatments incorporate the maintain-
(C) tertiary low-salinity polymer flood. (Credit: From Torrijos, ing of stable rupture pressure of gel. Another key issue
P., Iván, D., Puntervold, T., Skule Strand, Austad, T., Bleivik, for the successful deployment is the gel swelling
T. H., et al. (2018). An experimental study of the low salinity affecting the fluid flow. The salinity difference between
smart water e polymer hybrid EOR effect in sandstone gel network and aqueous phase might influence the de-
material. Journal of Petroleum Science and Engineering, 164, gree of swelling. Brattekås, Graue, and Seright (2016)
219e229. https://doi.org/10.1016/j.petrol.2018.01.031.)
experimentally investigated the effects of the salinity
on the blocking performance of conventional polymer
breakthrough time by 22% and are attributed to higher gel, Cr(Ⅲ)-acetate HPAM gels. They constructed the
retention of polymer by a factor of 5 in conventional water-wet fractured core plugs and placed the formed
polymer flood than LSPF. Secondly, the long-term injec- gels, which are composed of 5000 ppm of HPAM and
tivity test monitors the stabilized pressure profiles of 427 ppm of Cr(Ⅲ)-acetate, in the fracture core plugs.
conventional polymer flood and LSPF. The LSWF for The gel solvent is the formation water of salinity with
150 PV follows the conventional polymer flood for 79,170 ppm, and the high-salinity formation water is
130 PV. Before the initiation of LSPF, high-salinity obtained from the North Sea chalk reservoir. In the frac-
and low-salinity brines are flooded to exclude the uncer- tured cores with formed gel, four different saline brines
tainty. The test results in the higher differential pressure are flooded. Including formation water, the three low-
for conventional polymer flood and lower differential salinity brines have the salinities of 1,000, 500, and
pressure for LSPF, which means the improved injectivity 0 ppm as NaCl. The n-decane as oil is subject to the
is obtained for LSPF. This observation is contrast with experiment. In the system, the five sets of coreflooding
the observation in the carbonate reservoirs (AlSofi, using the brines measure the differential pressure across
Wang, & Kaidar, 2018). Unsal et al. (2018) explained the matrix and fracture as well as production rate. For
that the increasing injectivity of polymer flood with the three sets of coreflooding, each test is designed
low-salinity makeup brine in sandstone is attributed with five cycles of injection, and differential pressure
to the role of divalent ions. The higher effluent concen- and production rates are measured (Fig. 4.14). Firstly,
tration of divalent cations for LSPF over that for formation water is injected and low-salinity water