Page 75 - Formation Damage during Improved Oil Recovery Fundamentals and Applications

Low-Salinity Water Flooding: from Novel to Mature Technology 57

reservoir is known to influence the effectiveness of polymer injection
(Chiappa et al., 1999). This approach is expected to reduce the viscous
fingering effect of water flow within the reservoir and achieve better
sweep efficiency from the displacement process.
The results showed, consistent with other studies mentioned, that
LSWF is more efficient if commenced in secondary recovery mode.
Synergistic benefits were recorded by combining LSWF with polymer
(and nanosized polymer) injection. These were most effective when the
process commenced at initial reservoir oil saturation, achieving more than
50% reduction in residual oil saturation after the secondary recovery
mode waterflood, even using low (300 ppm) concentrations of polymer.
Shiran and Skauge (2013) attributed the beneficial effects to improved
banking of low-salinity mobilized oil with only a slight change in
mobility ratio.

2.11.3 LSWF combined with CO 2 water-alternating gas
injection
Through experimental core-flooding studies of wettability impacts during
conventional high-salinity water flooding (formation water followed by
sea water) followed by CO 2 flooding on North Sea reservoirs at tempera-

tures ranging from 50 C to 130 C, Fjelde and Asen (2010) have demon-
strated alterations to more water-wet conditions. After the third-phase
water-alternating gas (WAG) cycle residual oil saturation were reduced to
between 3% and 5%, demonstrating the effectiveness of the reservoir
sweep achieved by this combination. Zolfaghari et al. (2013) conducted
core-flood experiments. Based on a series of core-flood experiments
combining LSW with CO 2 in a WAG injection system, they reported an
incremental oil recovery of up to 18% OOIP.
Dang et al. (2016) evaluated the merits of combining LSW with CO 2
injection in a hybrid CO 2 -LSWAG process using 1D and full-field
simulation models combining ion exchange and reservoir geochemistry.
A secondary-mode LSW followed by tertiary-mode CO 2 -LSWAG model
outperformed high-salinity WAG, standalone LSWF, and continuous
CO 2 flooding models. Sensitivity cases for the models were used to iden-
tify the effects of solubility of CO 2 in various injected-water salinities,
dissolution of carbonate minerals, ion exchange, wettability alteration,
and clay distribution. CO 2 -LSWAG was simulated at full-field scale for
the North Sea Brugge oil field sandstone reservoir (Peters et al., 2009)