Page 91 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

CHAPTER 4 Hybrid Chemical EOR Using Low-Salinity and Smart Waterflood 83

on the oil recovery. This study proposed the two injec- In addition, the placing pressure of PPG and fracture
tion scenarios of coinjection of PPG and LSWF and suc- width are investigated. The placing pressure of PPG indi-
cessive injection of LSWF following PPG. The first cates the maximum pressure to inject PPG for each exper-
injection scenario is designed as pre- and postflush in- iment. Both the PPG placing pressure and fracture width
jection using 1% NaCl brine and various PPG injections slightly or negligibly affect the oil recovery and residual
with 0.01%, 0.1%, and 1% NaCl brines. Firstly, in the resistance factor.
displacement tests using oil-wet carbonate rocks, the re- Alhuraishawy and Bai (2017) published another
sidual resistance factor of coinjection of LSWF and PPG experiment of the first injection scenario, coinjection
is evaluated by varying the salinity of gel solvent. The of PPG, and LSWF. The microgel with mesh size of
PPG with NaCl brine of 0.1% shows the highest resid- 20e30 is used for the PPG injection in this study. The
ual resistance factor and that with NaCl brine of light crude oil of 36 degrees API and oil-wet Indiana
0.01% follows the next. The waterflood after the coin- limestone are prepared for the displacement experi-
jection scheme shows the higher injecting pressure ments. Firstly, swelling ratio measurements calculate
than the waterflood before the coinjection because of the swelling ratio of the dry microgel varying the solvent
the residual resistance factor by gel blocking. The sensi- with different brines (1%, 0.1%, and 0.01% NaCl). The
tivity of swelling ratio of PPG by salinity is observed. swelling ratio is defined as the difference between the
The low salinity condition relatively shows the higher initial weight of dry microgel and the weight of fully
resistance factor indicating higher gel swelling. Howev- swollen gel divided by the initial weight of dry gel.
er, there is an optimum salinity condition to maximize The increasing swollen gel is visualized as salinity of
the residual resistance factor. Next experiment investi- brine decreases (Fig. 4.15). The various fractured
gates the second scenario of hybrid process. It is
designed to apply LSWF following PPG with 1.0%
NaCl brine. The PPG with 1.0% NaCl solvent is fol-
lowed by the 1% NaCl brine as postflush process. The
residual resistance factor after the injection is estimated
by 9.2. Successively, chasing waters of 0.1% NaCl brine
and 0.01% NaCl brine are injected after the postflush.
The residual resistance factor after the chasing LSWF
using 0.1% NaCl brine increases up to 104, which indi-
cates the low salinity condition reswells the gels.
Despite high-saline gel solvent, the injection of low-
salinity water significantly increases the residual resis-
tance factor. The second chasing LSWF using 0.01%
NaCl brine rises the residual resistance factor up to
130. It is clear that low-salinity water injection as
chasing water injection confidently improves the resis-
tance factor of gel treatment regardless of salinity of
gel solvent. The higher residual resistance factor of
LSWF rises the injection pressures as well as oil recovery.
To quantify the wettability modification effect during
the hybrid process of low salinityeaugmented gel treat-
ment, same displacement test using the water-wet rock
is carried out. The comparison between the tests using
oil-wet and water-wet rocks captures a couple of observa-
tions. The injection of 1% NaCl brine after PPG injection
produces higher residual resistance factor in the water-
wet system than in the oil-wet system. However, the
chasing water injection of 0.1% NaCl brine results in re- FIG. 4.15 Increasing swollen gel with a decrease in salinity.
sidual resistance factor of 42 for the water-wet rock and (Credit: From Alhuraishawy, A. K., & Bai, B. (2017). Evaluation
104 for the oil-wet rock. The chasing LSWF modifies the of combined low-salinity water and microgel treatments to
oil-wet rock toward strongly water-wetness, and it negli- improve oil recovery using partial fractured carbonate
gibly changes the wetness of water-wet rock, which is in models. Journal of Petroleum Science and Engineering, 158,
line of preliminary spontaneous imbibition tests. 80e91. https://doi.org/10.1016/j.petrol.2017.07.016.)