Page 127 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

CHAPTER 5 Hybrid CO 2 EOR Using Low-Salinity and Smart Waterflood 119

analyze the effect of initial wetness. Three different brines also implies no formation damage of fines migration,
include the formation brine of 174,156 ppm TDS, precipitation, or plugging. Secondly, the immiscible
seawater of 54,680 ppm TDS, and NaCl brine of CO 2 WAG processes using seawater and low-salinity
5000 ppm TDS as low-salinity water. In the system of water are investigated (Fig. 5.4). The coreflooding of
crude oil/sandstone/brine, the low-salinity water shows CO 2 WAG process uses only unaged core, which screens
the lowest contact angle and seawater shows the highest out the wettability modification effect of LSWF. In the
contact angle for both aged and unaged cores. During the comparison between conventional CO 2 WAG using
measurement, the temperature of the system is increased seawater and LS-CO 2 WAG processes, conventional
to examine the effect of temperature on the contact CO 2 WAG shows the slightly higher oil recovery
angle. The higher contact angle with an increase in over the LS-CO 2 WAG. It is explained that the slight
temperature is observed. Interestingly, the formation increment by 2.93% is attributed to the salting-out
water condition has lower contact angle than the effect, which is similar to the observations of Jiang
seawater despite higher salinity, i.e., the less water- et al. (2010). The higher solubility of CO 2 in low-
wetness in formation water condition than seawater salinity water results in the less contact between oil
condition. It is explained that the seawater, which has and CO 2 . The less contact leads to the less contribution
the relatively higher fraction of divalent cations of immiscible mechanism of CO 2 injection on the oil
compared with formation water, results in the bridging production. The fluctuating pressure drop is observed
between the anionic surfactant, i.e., negative polar during the period of CO 2 injection for both conven-
component, of crude oil and the significant amount of tional CO 2 WAG and LS-CO 2 WAG processes. It is
divalent cations on the rock surface. Another experiment estimated to the result of CO 2 dissolution in water.
measures a dynamic contact angle in the system of crude This study clearly confirmed the effect of salinity-
oil/brine/CO 2 /unaged rock for 24 h. Because of the dependent CO 2 solubility on the performance of
interactions between oil and CO 2 , and oil and brine, LS-CO 2 WAG process in water-wet system. Because
the measured contact angle has some fluctuations. After this study lacks the investigation of LS-CO 2 WAG
some time to be stabilized, the consistent tendency process using oil-wet cores, it is not clarified whether
between contact angle and brine type is similar to the LS-CO 2 WAG process secures the mechanism of LSWF
previous measurements. The results of contact angle or not.
measurements indicate that low-salinity water results in Ramanathan, Shehata, and Nasr-El-Din (2016)
the more water-wet rock samples. The seawater brine reported the further investigations of CO 2 WAG process
shows the more oil-wet rock samples in both systems with various brine types. The axisymmetric drop shape
representing waterflood and CO 2 WAG process. analysis measures the IFT of the brine/crude oil/N 2
In a number of coreflooding experiments, the and brine/crude oil/CO 2 systems. The same brines of
secondary CO 2 WAG processes and waterflood using formation brine, seawater, and low-salinity water are
low-salinity water and seawater are analyzed. The exper- prepared. It is clearly measured that high-salinity brine
iments also use both the aged and unaged cores to shows the higher density, and higher temperature de-
investigate the effect of initial wetness. Firstly, the creases the density of brine. In the system of brine/crude
conventional waterflood using seawater and LSWF are oil/N 2 , the equilibrium IFT is measured at various
investigated, considering the initial wetness of cores. temperature and immiscible conditions. The low-
In the system of unaged core, the effect of LSWF is salinity water shows the highest IFT and seawater results
hardly observed. Instead, a slight higher oil recovery is in lowest IFT regardless of temperature condition.
observed in conventional waterflood compared with Because the effect of monovalent ions on interfacial
the LSWF. In the system of aged core, which is initially activity between oil and water is weak and interfacial
more oil-wet condition, the higher oil recovery by 14% active substances are oil-soluble, it is not able to
is observed for the LSWF than the conventional water- influence the interfacial interactions (Bai, Fan, Nan, Li,
flood. In addition, the LSWF produces the significantly & Bao-Shi, 2010). The effect of temperature on the IFT
higher oil recovery in aged core system than unaged shows a similar trend of increasing IFT with an increase
core system. However, the conventional waterflood in temperature. Referring the experiments of Hjelme-
shows the insignificant change of oil recovery between land and Larrondo (1986), there will be a lower concen-
both systems. These observations are in line with the tration of the surface-active components at the brine/oil
results of contact angle measurement. It is obvious interface at higher temperatures. As a result, higher tem-
that the LSWF is effective to modify the wettability of perature condition might contribute to the higher IFT.
oil-wet rock system. The measured pressure drop The dynamic interfacial tension is measured in the