Page 86 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

78 Hybrid Enhanced Oil Recovery using Smart Waterflooding

prepared. The Arabian Gulf seawater of 36,170 ppm that LSPF enables to improve heavy oil recovery from
TDS and the diluted version of the seawater by a factor sandstone core. Initial wettability and clay content are
of 10, i.e., low-salinity water, are used. The following ex- also of importance to employ wettability modification
periments investigate the cores from the Berea and low effect.
clay content Bentheimer sandstones. The polymeric so- Torrijos et al. (2018) also investigated the applica-
lution of LSPF is prepared with HPAM of 5000 ppm tion of LSPF in terms of the initial wetting, wettability
and low-salinity water. alteration with improving microscopic sweep efficiency
Firstly, IFT measurements between two brines and and redistribution of oil, and mobility of oil within the
heavy oil clearly provide the reduction of IFT up to sandstone core. The stabilized crude oil has AN of
20 dyne/cm as the salinity decreases. It is explained 0.10 mg KOH/g and BN of 1.80 mg KOH/g. The forma-
that the reduction is not enough to modify wettability tion water has the salinity of 100,000 ppm TDS,
and increase oil production. This conclusion agrees to seawater has salinity of 33,390 ppm TDS, and low-
the extensive studies of LSWF. Varying the salinity of salinity water consisting of only NaCl has salinity of
brine, the contact angles in Bentheimer and Berea sand- 1000 ppm TDS. The polymeric solution of LSPF is pre-
stones are measured. In the formation water and pared by dissolving the 1000 ppm of Flopaam 3630s
seawater conditions, the wettability of Berea sandstone polymer into the low-salinity water of 1000 ppm
is determined as intermediate wetness with contact NaCl brine. Although the brines of formation water
angle of 90 degrees. Switching the brine with low- and low-salinity water have the low pH of 5.5 and
salinity water drops contact angle down to 75 degrees, 5.7, the fluids of seawater and low-salinity polymeric
which indicates the wettability modification of Berea solution have the high pH of 7.8. Three sets of sand-
sandstone. For the low clay content Bentheimer sand- stone cores are subject to the coreflooding experiments.
stone core, the contact angle of 70 C is measured in A majority of the sandstone cores are composed of

the formation water and seawater conditions and the quartz, albite, and illite. Because the surface area and
wettability is determined to be close to water-wetness. CEC of sandstone are the crucial factors to determine
The low-salinity water only decreases the contact angle the degree of low-salinity waterflood effect, the surface
by 5 degrees; therefore, it hardly modifies the wetta- area of core materials is measured using Brunauer-
bility of Bentheimer core. The z-potential measurement Emmett-Teller (BET) surface area measurement. The
draws the similar conclusions, which are obtained from cores have the equivalent surface area of
2
the contact angle measurement. The seawater results in 1.81 0.02 m /g. Before the description of LSPF exper-
the positive value of z-potential, and the significant iments, the study summarized the previous experi-
reduction in z-potential is obtained for the low- mental results of LSWF.
salinity water. The low-salinity water also decreases The experiments of imbibition test observe the
the z-potential of Bentheimer core compared with the increasing oil recovery with an increasing pH up to 9
seawater. The magnitude of the z-potential reduction when the injecting brine is switched from secondary for-
in Bentheimer core is highly less than that in Berea mation water to the tertiary low-salinity water. It is
core. A number of corefloodings are designed as second- explained that initial wettability is the fractional
ary mode waterflood or LSWF and tertiary mode of con- wetness and suggested that the observation is in line
ventional polymer flood or LSPF. Using the with the suggested mechanism of the pH increase modi-
intermediate-wet Berea sandstone core, it is observed fying wettability. The increasing pH, alkaline condition,
that the secondary LSWF shows higher oil recovery by LSWF is favorable to the deprotonation of acidic and
than the secondary waterflood. The tertiary mode of basic polar organic components of oil. The interaction
LSPF also enhances the oil recovery over the tertiary of the deprotonated organic components onto the
mode of conventional polymer flood or secondary negatively charged clay surface decreases shifting wetta-
mode of LSWF. It is obvious that the wettability modi- bility toward more water-wet. Recalling the experiments
fication mechanism during LSWF and LSPF is effective of tertiary LSWF process, the deployment of hybrid
in intermediate-wet Berea sandstone. In contrast, the ef- LSPF following the secondary LSWF is experimentally
fect of wettability modification is not observed in both performed. In the experiment, the secondary LSWF pro-
processes of secondary LSWF and tertiary LSPF for the cess recovers the 66% of OOIP, which shows the 17%
water-wet Bentheimer sandstone core. This contrasting higher recovery of OOIP compared with the previous
observation between Berea and Bentheimer sandstones results of tertiary LSWF process. Following the suggested
is comparable with the observations from contact angle mechanism, the higher oil recovery of secondary LSWF
and z-potential measurements. This study concluded process should use the higher pH condition over tertiary