Page 134 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

126 Hybrid Enhanced Oil Recovery using Smart Waterflooding

carbonate rock surface is positively charged. In the test, light oil recovery because of higher solubility of CO 2
the system of carbonated rock-deionized water shows in lighter oil. For the heavy oil reservoir, the mechanism
the z-potential of 2.27 mV. Because the oil has nega- of viscosity reduction might be main contributor on the
tively charged acidic molecules, the addition of crude oil recovery controlling interfacial tension. Therefore,
oil into the brine-rock system changes the z-potential the LS-CWI is the promising EOR process in carbonate
toward more negative. The system of carbonated reservoir.
rock-deionized water-crude oil has 37.9 mV. The NMR test and ICP analysis investigate the
Following the double layer expansion and ion exchange interaction of carbonate rock-brine. The NMR test
phenomena, the LSWF or smart waterflood should estimates the porosity distribution of the three different
change the surface charge of the system to positive cores, which are used in three coreflooding experiments.
value. The seawater, low-salinity water, modified The porosity distributions of carbonate cores are esti-
seawater, and modified low-salinity water show the mated before and after coreflooding. After coreflooding
negative surface potentials of rock-brine-crude oil test, the overall porosities are increased by 0.5%, 1.95%,
system. However, only modified seawater brine having and 2.31%, respectively. The increase in porosity
four times higher concentration of sulfate shows the is attributed to the carbonate rock dissolution. Mostly,
positive potential in the system of rock-brine-oil. Based the carbonate mineral dissolution increases the
on the z-potential measurement, the modified seawater distribution of macroscopic pore. Some reduction in
is determined as the smart water and low-salinity water. the distribution of microscopic pore is the result of
Using the smart water, the carbonated water, which is precipitation of sulfate ions. As well as the injection of
fully CO 2 -saturated water, is prepared at the experi- different ionic composition of brine, the mineral
mental condition of coreflooding, 350 psi and 100 C. dissolution also changes the concentration of in situ

Neglecting the effect of salinity of water, the CO 2 solu- and effluent brines. The ICP analysis measures the
bility in water is referred from the work of Wiebe and effluent concentrations of potential-determining ions
2þ
Gaddy (1940). At the experimental condition, the 6 cc of Mg , SO 4 2 , and Ca . The effluent concentration
2þ
of CO 2 is determined to dissolve in 1 cc of water. of SO 4 2 is determined to be less than injecting concen-
Once the brine and estimated CO 2 are stored in the tration of SO 4 2 . The reduced concentration of SO 4 2
floating piston cylinder, the fluids are pressurized up implies the precipitation and deposition of sulfate-
to the 350 psi to dissolve CO 2 into brine. As the CO 2 associated mineral or adsorption on the rock surface.
dissolves in water, the pH of the brine decreases. The interpretation agrees with the observation of
Three coreflooding experiments are designed to increasing distribution of microscopic pore from NMR
deploy in the sequence of waterflood using seawater, test. In addition, higher concentration of Ca 2þ is
LSWF using modified seawater, and LS-CWI using observed in the effluent brine than injecting brine
modified seawater in carbonate cores. The permeability because of carbonate mineral dissolution. The observa-
of cores ranges from 1.59 to 20.25 md. The tertiary tion also corresponds to the increasing distribution
recovery of LSWF varies from 9.4% to 0.66%. The of macroscopic pore of NMR test. In terms of concen-
LS-CWI increases the oil recoveries by 5.7%e13.9%. tration of Mg 2þ , the consistent interpretation is hardly
The recovery efficiency of LS-CWI is significantly higher drawn. Kilybay et al. (2017) reported the further
compared with other processes. In addition to securing analysis of rock dissolution using the carbonate rock
the wettability modification following the LSWF powders at various pH conditions. As the pH of brine
mechanism, it is suggested that three main mechanisms decreases, the decreased weight of carbonate rock
occur in the LS-CWI such as swelling and coalescence powders indicates mineral dissolution. These studies
of trapped oil ganglia, local flow diversion, and oil (Kilybay et al., 2016, 2017)have demonstratedthe
viscosity reduction. Both the swelling and coalescence significant EOR potential of LS-CWI process in
of trapped oil ganglia and oil viscosity reduction might carbonate rocks and interactions in the rock-brine-oil
improve the macroscopic sweep efficiency. In addition, contributing the EOR potential.
the carbonated water has higher viscosity than normal A couple of numerical studies (Lee, Jeong, & Lee,
water, and the higher viscosity of injecting carbonate 2017; Lee & Lee, 2017) have investigated the LS-CWI
water contributes to improve mobility ratio. When the and observed the synergy of mechanism of LSWF and
carbonated water contacts oil, the mass transfer of CWI. Main contributions of LS-CWI on the EOR poten-
CO 2 between carbonate water and oil reduces the oil tial are the oil viscosity reduction, oil swelling, and
viscosity. It is suggested that the mechanism of swelling wettability modification. In addition, the other studies
and coalescence of trapped oil ganglia is dominant in (Lee, Kim, & Lee, 2017a, 2017b) have advanced the