Page 129 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

CHAPTER 5 Hybrid CO 2 EOR Using Low-Salinity and Smart Waterflood 121

formation water and seawater. The seawater shows the higher recovery is observed in LSWF injecting
highest contact angle. The observations indicate the po- NaCl brine. Two coreflooding experiments injecting
tential of LS-CO 2 WAG to modify wettability toward CO 2 and NaCl brine are investigated in immiscible
more water-wet condition. condition. The injection processes are designed to apply
Two coreflooding of conventional CO 2 WAG and LS- the secondary LSWF using the NaCl brine and tertiary
CO 2 WAG is performed using aged core (Fig. 5.5). CO 2 injection, and secondary LS-CO 2 WAG using
Although conventional CO 2 WAG recovers oil up to NaCl brine. In the first coreflooding, the secondary
76.1%, the LS-CO 2 WAG recovers by 97.7%. Recalling LSWF using NaCl brine recovers 36.32% of oil and
the previous experimental observation of CO 2 WAG tertiary immiscible CO 2 injection increases the recovery
processes using unaged core (Ramanathan et al., by 7.7%. The second coreflooding of LS-CO 2 WAG
2015), the opposite observation is reported in the study using NaCl brine produces oil recovery up to 66.84%,
(Ramanathan et al., 2016). The performance of LS-CO 2 which is 22.82% higher than the first coreflooding
WAG process obviously prevails the performance of result. Interestingly, the continuous oil production is
conventional CO 2 WAG process in aged core system. observed for LS-CO 2 WAG, but not for the secondary
The 36% more oil is recovered despite salting-out effect. LSWF and tertiary CO 2 injection. It is concluded that
Higher oil recovery of LS-CO 2 WAG process than LS-CO 2 WAG process introduces the synergy of LSWF
conventional CO 2 WAG process corresponds to contact and immiscible CO 2 injection on oil production. In
angle measurement. In the aged core system, the usage addition, the WAG process achieves an optimized
of low-salinity water is favorable to the both waterflood sweep efficiency to maximize the synergy of LSWF
(Ramanathan et al., 2015) and CO 2 WAG process and immiscible CO 2 injection.
(Ramanathan et al., 2016). Lastly, the profiles of satura-
tion and porosity in the four cores, which are used in
NUMERICAL SIMULATIONS
the coreflooding experiments of conventional CO 2
WAG process and LS-CO 2 WAG process, are estimated Dang, Nghiem, Chen, Nguyen, and Nguyen (2013)
by CT scanning method. Two cores are aged cores tried to combine the LSWF and CO 2 WAG processes
used in the work of Ramanathan et al. (2016) and numerically and constructed one-dimensional sand-
last two cores are unaged cores used in the work of stone model. The numerical model of LS-CO 2 WAG
Ramanathan et al. (2015). Different profiles in the process incorporates aqueous reactions, mineral disso-
saturation distribution and average porosity are clearly lution of calcite, and cation exchange. The study
observed. Both studies have demonstrated the assumed the mechanism of LSWF as the wettability
synergetic potential of immiscible LS-CO 2 WAG process modification changing relative permeability. The
through comprehensive experiments. It is concluded wettability modification is assumed to be attributed
2þ
that the LS-CO 2 WAG is able to introduce both effects to the cation exchange of Ca . In the previous experi-
of LSWF and CO 2 injection depending on the initial mental studies, it is clearly observed that the CO 2
wetness. Although the low-salinity water is unfavorable solubility in brine influences the performance of CO 2
to reduce IFT, it is effective to modify the wettability of WAG process. Once the injected CO 2 dissolves into wa-
less water-wet core toward more water-wet. Although ter, the dissolved CO 2 dissociates to produce hydrogen
the salting-out effect is slightly unfavorable to the con- ions, i.e., lower pH. These reactions are implemented in
tacting between oil and CO 2 , the effect of immiscible the numerical model of LS-CO 2 WAG process. The
CO 2 injection sufficiently enhances oil production. secondary waterflood is applied until 200 days. The per-
Therefore, the LS-CO 2 WAG process is a promising formance of tertiary LS-CO 2 WAG process is compared
hybrid EOR process securing synergy. with the conventional waterflood, LSWF, CGI, and
Kumar, Shehata, and Nasr-El-Din (2016) reported conventional WAG process. The LS-CO 2 WAG process
produces more oil than other processes. The secondary
the coreflooding experiments of LSWF and LS-CO 2
WAG processes. The experiments of LSWF examine application of LSWF ahead of tertiary LS-CO 2 WAG
the promising ionic composition of brine to introduce produces more oil. The higher oil recovery of LS-CO 2
the mechanism of LSWF into LS-CO 2 WAG process. WAG is a result of combination of wettability modifica-
The brines of formation brine, seawater, and three types tion and miscibility effects. Especially, the injection
of low-salinity water are prepared. The low-salinity of CO 2 decreasing pH possibly increases the Ca 2þ
waters are NaCl brine, KCl brine, and MgCl 2 brine, concentration of in situ brine. It is attributed to the
and they equally have 5000 ppm TDS. In the experi- calcite mineral dissolution in lower pH. The higher
ments of secondary waterflood using the brines, the concentration of Ca 2þ increasing cation exchange of