Page 125 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

CHAPTER 5 Hybrid CO 2 EOR Using Low-Salinity and Smart Waterflood 117

the mixture of CO 2 -water following CO 2 slug at the less reduction in tertiary recovery. Although the unfa-
displacement front is effective to contact the bypassed vorable effect of low-salinity water on the performance
oil by the CO 2 slug. The mixture of CO 2 -water improves of tertiary CO 2 WAG process is observed, the applica-
the displacement efficiency and increases the oil tion of secondary LSWF can enhance the oil recovery
recovery of the injection process of CO 2 and water. ahead of tertiary CO 2 WAG.
Jiang, Nuryaningsih, and Adidharma (2010) A couple of studies (Teklu et al., 2014, 2016)
analyzed the effect of salinity as well as divalent cation have investigated the combination of miscible and
on the coreflooding of miscible CO 2 WAG process using immiscible CO 2 injection and low-salinity waterflood.
synthetic oil, which is composed of n-decane and The displacement experiments are designed with one
n-hexadecane, and crude oil. Two different types of cycle CO 2 WAG process after secondary waterflood. In
connate brines are prepared: NaCl brine of 1000 ppm, the CO 2 WAG process, CO 2 injection follows the
mixing brine of NaCl of 4000 ppm, and CaCl 2 of LSWF. Before the coreflooding experiment, MMP,
4000 ppm. The synthetic and crude oils have MMPs as IFT, and contact angle are measured under various

1673 and 2541 psi at 60 C, respectively. In the core- conditions. Brines of connate water, seawater, three
flooding experiment, the CO 2 WAG process is applied cases of synthetic low-salinity water, and deionized
in the tertiary mode after the secondary waterflooding. water are prepared in the descending salinity order.
The miscible process during CO 2 WAG is achieved by Experimentally, the rising bubble apparatus (RBA)
making system to be at 20% higher pressure than the tool estimates the MMP of crude oil and CO 2 as
MMP. During the CO 2 WAG, the slug sizes of both 2500 psi. The numerical approach using multiple
CO 2 and water are 0.25 PV and the volumetric WAG mixing cell (MMC) calculates the MMP as 2470 psi
ratio is set as 1:1. being comparable with the experimental determina-
The first set of coreflooding using the synthetic oil tion. Pendant drop method determines the IFTs of
quantifies the effects of salinity and divalent cations crude oil and the various brines. As the salinity de-
on the oil recovery of secondary waterflood, tertiary creases, the IFT slightly increases. The experiment of
CO 2 WAG, and chasing waterflood. The core is initially captive oil-bubble contact angle measures the contact
saturated with the NaCl brine of 1000 ppm TDS. In angle in the various systems of crude oil/brine/rock.
the secondary waterflood, the increasing salinity of Three rocks of different mineralogy are prepared,
injecting brine from 1000 to 32,000 ppm TDS results including carbonate, Berea sandstone, and Three Forks.
in the negligible change in oil production and 32% of Preliminary, the effect of initial wetness is investigated
oil recovery is observed. The negligible effect of salinity by using aged cores or unaged cores. Regardless of the
indicates that the mechanism of LSWF hardly exists. aging status of cores, the consistent tendency is
During the period of tertiary CO 2 WAG, the slight observed of the decreasing contact angle with a decrease
increase of oil recovery by 5.6% is observed with an in salinity. Additional measurement of contact angle
increasing salinity. The observation is in contrast to using the aged cores analyzes the contact angle in the
the experimental observations of Aleidan and Mamora system of crude oil/mixture fluid of CO 2 and brine/
(2010). The improved oil recovery in higher salinity rock at miscible condition of 2500 psi (Fig. 5.3). It is
condition explains that the salting-out effect, which clearly observed that the contact angle is decreasing
indicates the less solubility with an increase in salinity, with a decrease in salinity. The additional IFT measure-
makes more CO 2 to be miscible with oil. In another ment in the system of crude oil/mixture fluid of CO 2
coreflooding experiment, the effect of divalent cation and brine also results in the slight reduction in IFT by
is investigated and the negligible effect of divalent adding CO 2 at atmospheric condition. The results of
cation is observed on the oil recovery. In the second IFT and contact angle measurements imply that
set of coreflooding using crude oil, the role of salinity the wettability can be improved by the usage of
on the oil recovery of secondary waterflood and tertiary low-salinity water and addition of CO 2 . However, the
CO 2 WAG is investigated. The core is saturated with IFT reduction is only effective by the addition of CO 2 .
connate brine of NaCl of 20,000 ppm and CaCl 2 of LS-CO 2 WAG is determined to introduce both
10,000 ppm. In contrast to the first set coreflooding wettability modification and miscible effects.
using synthetic oil, the oil recovery of waterflood The EOR potential by the LS-CO 2 WAG is evaluated
increases with a decrease in salinity. The trend of through the coreflooding in miscible and immiscible
waterflood recovery depending on the salinity can be conditions. The two sets of coreflooding using carbonate
attributed to the effect of LSWF. However, the lower- cores are carried out in the miscible condition. The
salinity water injection of CO 2 WAG shows the slightly preflush of LSWF produces the additional oil recovery